Distributed multi-channel cognitive mac protocol

ABSTRACT

A method includes sending a message from a first to at least one second cognitive radio apparatus to determine a channel to be used for sending data from the first to the second radio apparatus, the message sent over a first channel and comprising an advertisement of at least one second channel for use in sending the data from the first to the second radio apparatus, the advertisement comprising a corresponding proposition/evaluation bit for each second channel, receiving a reply from the second radio apparatus over the first channel, comprising an acceptance of one of the second channels with the corresponding proposition/evaluation bit, a rejection of the second channel and an advertisement of a third channel, or a rejection of the second channel without an advertisement of a third channel, and transmitting the data from the first to the second radio apparatus over an agreed upon second or third channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/450,281, filed 3 Aug. 2014, which is a continuation of U.S.application Ser. No. 12/082,361, filed 4 Sep. 2008, the disclosures ofwhich are incorporated herein by reference in their entirety.

FIELD

The exemplary and non-limiting embodiments disclosed herein relategenerally to wireless communication systems, methods, devices andcomputer programs and, more specifically, relate to cognitive radioapparatus and to wireless systems that are operable with cognitive radioapparatus.

BACKGROUND

Opportunistic radio resource management (RRM) schemes have recentlyreceived extensive attention in scientific literature and technologicalfields. One possible area for which opportunistic RRM can be effectiveis IEEE 802.11-based wireless local area networks (LANs). Existing IEEE802.11 based systems suffer from inefficient medium access strategies,namely distributed coordination function (DCF), point coordinationfunction (PCF), and their corresponding amendment supporting quality ofservice (QoS). Furthermore, it is expected that problems will arise dueto lack of sufficient frequency opportunities, due at least to the factthat frequency regulations have not efficiently allocated diversefrequency bands. Consequently, cognitive radio, frequency agile, andopportunistic RRM schemes aim to address the aforementioned criticalproblems in an optimized fashion, resulting in better spectrumutilization and fair radio resource allocation to associated wirelessentities.

SUMMARY

In a first non-limiting aspect thereof the exemplary embodiments providea method that includes sending a message from a first cognitive radioapparatus to at least one second cognitive radio apparatus, the messagebeing sent over a first communication channel and comprising anadvertisement of at least one second communication channel for use insending data from the first cognitive radio apparatus to the at leastone second cognitive radio apparatus. The method further includesreceiving a reply from the at least one second cognitive radio apparatusover the first communication channel, where the reply comprises one ofan acceptance of one of the at least one second communication channels,a rejection of the at least one second communication channel and anadvertisement of at least one third communication channel, or arejection of the at least one second communication channel without anadvertisement of at least one third communication channel. The methodfurther includes transmitting the data from the first cognitive radioapparatus to the at least one second cognitive radio apparatus over anagreed upon one of the second or third channels.

In another non-limiting aspect thereof the exemplary embodiments providea computer-readable medium that stores program instructions, theexecution of the program instructions resulting in operations thatcomprise sending a message from a first cognitive radio apparatus to atleast one second cognitive radio apparatus, the message being sent overa first communication channel and comprising an advertisement of atleast one second communication channel for use in sending data from thefirst cognitive radio apparatus to the at least one second cognitiveradio apparatus; receiving a reply from the at least one secondcognitive radio apparatus over the first communication channel, thereply comprising one of an acceptance of one of the at least one secondcommunication channels, a rejection of the at least one secondcommunication channel and an advertisement of at least one thirdcommunication channel, or a rejection of the at least one secondcommunication channel without an advertisement of at least one thirdcommunication channel; and transmitting the data from the firstcognitive radio apparatus to the at least one second cognitive radioapparatus over an agreed upon one of the second or third channels.

In a further non-limiting aspect thereof the exemplary embodimentsprovide a first transceiver for communication over a first communicationchannel; a second frequency agile transceiver for communication oversecond and third communication channels and a controller configurable tooperate the apparatus as a first cognitive radio apparatus and totransmit a message to at least one second cognitive radio apparatus. Themessage is transmitted over the first communication channel andcomprises an advertisement of at least one second communication channelfor use in sending data from the first cognitive radio apparatus to theat least one second cognitive radio apparatus. The controller is furtherconfigurable to receive a reply from the at least one second cognitiveradio apparatus over the first communication channel, the replycomprising one of an acceptance of one of the at least one secondcommunication channels, a rejection of the at least one secondcommunication channel and an advertisement of at least one thirdcommunication channel, or a rejection of the at least one secondcommunication channel without an advertisement of at least one thirdcommunication channel. The control unit is further configurable totransmit the data to the at least one second cognitive radio apparatusover an agreed upon one of the second or third channels.

BRIEF DESCRIPTION OF THE DRAWINGS

In the attached Drawing Figures:

FIG. 1A shows a high level block diagram of a cognitive radio systemhaving a plurality of STAs and a BSS;

FIG. 1B shows a simplified block diagram of a two-transceiver STA;

FIG. 2A shows the current channel numbering scheme of IEEE 802;11 a,FIG. 2B shows the case of the IEEE 802;11b and IEEE 802;11g, 2;4 GHzband, while FIG. 2C shows the IEEE 802;11y 3 GHz band;

FIG. 3 shows a position of a new Channel Information (CI) field incontrol frames;

FIG. 4 shows a generic format of the Channel Information (CI) field;

FIG. 5 shows a generic sub-field format of the Channel Control (CC)field shown in FIG. 4;

FIGS. 6, 6A and 6B show Reason Code Bit Patterns that pertain to theReason Code sub-field of FIG. 5;

FIG. 7 illustrates possible frame exchange scenarios for PS mode enabledand PS mode disabled cases;

FIG. 8 illustrates Channel Control (CC) inclusion within the exchangedcontrol frames;

FIG. 9 shows a simple example of a task list;

FIGS. 10A-10D describe four modes I, II, Ill and IV, respectively, thatare related to a non-ISM band convergence concept;

FIG. 11 shows a “Reception” task merging procedure for the Task Listshown in FIG. 1B;

FIG. 12 shows a “Transmission” task merging procedure for the Task Listshown in FIG. 1B;

FIG. 13 illustrates sub-domains of a LSEChannel Time Index Domain;

FIG. 14 shows an Information Element for Primary User AppearanceReporting;

FIG. 15 illustrates a Channel Information Database, Management Entities,and Transient Zone;

FIG. 16 shows a Task List maintenance rule and strategy thataccommodates a single transceiver STA embodiment;

FIG. 17 shows a simplified block diagram of a two-transceiver cognitivemesh entity (CME);

FIG. 18 is a depiction of a Common Channel Framework (CCF) concept inIEEE 802;11s;

FIG. 19 shows an example of a permanent channel switching announcementusing a CHSW frame transmitted on the shared ISM channel;

FIG. 20A shows the eRTX frame format in a cognitive common channelframework (CCCF), while FIG. 20B shows the eCTX frame format;

FIG. 21 shows a Channel Switching (CHSW) frame format in the CCCF;

FIG. 22 depicts a channel switching information element (CHSWIE)structure in eRTX, eCTX, and CHSW frames;

FIGS. 23A and 23B are tables showing a Reason Code Bit Pattern (CHSWIEStatus=11) and a Reason Code Bit Pattern (CHSWIE Status=00);

FIG. 24 shows a channel reservation using eRTX and eCTX, for a casewhere the knowledge of the CSE concerning the LTRC of the CDE iscorrect;

FIG. 25 shows a channel reservation using eRTX and eCTX for a case whereonly the LTRC channel information of the CDE is included in the eRTX,while the knowledge of the CSE of the LTRC of the CDE is incorrect;

FIG. 26 shows the channel reservation using eRTX and eCTX when the CSEhas no a priori knowledge of the LTRC of the CDE;

FIG. 27 shows the channel reservation using eRTX and eCTX when theknowledge of the CDE of the LTRC of the CSE is incorrect;

FIG. 28 illustrates the eRTX CHSWIE possible configurations and thecorresponding Duration/ID and OLD sub-field setup;

FIG. 29 illustrates the eCTX CHSWIE possible configurations and thecorresponding Duration/ID and OLD sub-field setup;

FIG. 30 illustrates in detail the frame format of a SWinv control frameand its associated CHSWIE;

FIG. 31 illustrates exemplary message flow for a multicast temporarychannel switching use case;

FIG. 32 illustrates exemplary message flow for a Mode I multicastpermanent channel switching use case;

FIG. 33 illustrates exemplary message flow for a Mode II multicastpermanent channel (fast) switching use case;

FIG. 34 illustrates exemplary message flow for a combinedmulticast/unicast channel switching use case; and

FIG. 35 is a logic flow diagram that illustrates the operation of amethod, and a result of execution of computer program instructions, inaccordance with the exemplary embodiments.

DETAILED DESCRIPTION

The exemplary embodiments provide a novel distributed frequency agilemedium access control (MAC) protocol suitable for use in next generationwireless LANs, which furthermore have complete backwards compatibilitywith the legacy 802.11 systems. The enhanced MAC protocol is capable ofmulti-channel deployment of available frequency bands to coordinateconcurrent multiple data transmissions. Previous multi-channel MACprotocols for wireless LANs that have been proposed in the literaturegenerally make unreasonable assumptions, while being unable to addresstechnical problems concerning channel utilization and simultaneousinformation transmissions. In contrast, the exemplary embodimentsprovide an optimized MAC protocol, which is capable of addressing avariety of problems inherent in multi-channel systems, while being awareof primary users in different frequency bands using intelligentenvironmental information management entities.

The use of the exemplary embodiments also improve the channelutilization and capacity using the concept of cognitive radio and alsoreduce access delay due to more intelligent decision making proceduresused for link layer connection establishment. In addition, a concept ofwelfare enhancement (WE) is provided, that results in higher channelutilization and system throughput. Future extensions to the disclosedenhanced protocols may be simply incorporated, without requiring majorprotocol core code modification.

New fields for control/management frames are provided in such a way thatlegacy STAs are able to understand legacy fields while discarding thenewly added fields (and sub-fields). Legacy STAs are able to receive anddecode all frames generated by cognitive “smart” STAs except for thosefields dedicated and particularly designed for cognitive STAs. Thus,both legacy and new systems are able to work with each other. LegacySTAs are able to join cognitive BSSs and vice versa.

FIG. 1A shows a high level block diagram of a cognitive radio systemhaving a plurality of stations (STAs) 10, a basis service set (BSS) 12and a cognitive basis service set (CBSS) 14. Certain of the STAs 10 maybe cognitive STAs 10A, and others may be legacy (non-cognitive) STAs10B.

FIG. 1B shows a simplified block diagram of a cognitive STA 10A. In thisexample the cognitive STA 10A includes two wireless transceivers,specifically an ISM band (industrial, scientific, medical band)transceiver 20 and a cognitive transceiver 22. The STA 10A also includesa controller, such as at least one data processor (DP) 21 that operatesin accordance with a stored program in a memory 23. Execution of theprogram instructions results in the implementation of a MAC entity 26that is constructed and operated in accordance with the exemplaryembodiments. The cognitive STA 10A also includes transceiver associatedtask lists 24A, 24B (which may be collectively referred to as a tasklist 24), and other components and data structures as described indetail below.

Legacy IEEE 802.11 based wireless networks are currently capable ofoperation in certain dedicated ISM channels. As such, a need exists toenable next generation wireless LANs to operate in any frequency band,while being able to work and interact with existing legacy 802.11networks. For example, assume a case of an established legacy 802.11basic service set (BSS) 12 comprising associated 802.11 stations (STAs)10 working/collaborating with another cognitive basic service set (CBSS)14 which is able to provide additional network connectivity and packetforwarding to the legacy system. Further in this regard providingadditional network connectivity and packet forwarding to the legacy BSS12 mandates that the CBSS 14 operate at the same frequency band and ISMchannel as the existing legacy 802.11 system. This fact implies thatlegacy BSS 12 and CBSS 14 may be better combined with one another toproduce a global widespread 802.11 BSS. As a result, and in the same ISMchannel, there is provided a BSS 12 to which both legacy and cognitiveSTAs 10 are associated and cooperating with each other in differentways, e.g., packet forwarding, frame buffering, etc.

On the other hand, it is desirable to not congest the shared ISM channelwith those frames exchanged by cognitive STAs 10A. This becomes possiblewhen cognitive STAs 10A utilize non-ISM data channels other than theshared channel, which is utilized particularly by legacy 802.11 STAs 10.As a result, one may conclude that it is better for the shared ISMchannel to be utilized predominantly by legacy STAs 10B for management,control, and data exchange purposes, while the shared ISM channel isused only for management and control purposes for cognitive STAs 10A.

According to the foregoing, since both legacy and cognitive STAs 10 canbe associated to a common BSS 12 while using the same ISM channel formanagement/control purposes, consequently they are able to cooperate incontrol and management functions. Thus, it can be argued that frommanagement/control point of view, there is no difference between alegacy 802.11 STA 10B and a cognitive 802.11 STA 10A. On the other hand,and as pointed out, cognitive STAs 10A should preferably not use theshared ISM channel for their data communication. As a result, cognitiveSTAs 10A are strongly mandated to switch to another channel (referred toherein as a non-ISM channel) in order to perform their informationexchange. However, a problem that arises is how the receiving STA 10knows to which channel it should switch to enable the source STA 10 totransmit MSDU(s). In addition, a related problem is how the source STA10 recognizes in which channel its intended receiver is waiting toreceive its targeted MSDU(s).

The cognitive destination STA 10A should be able to determine and switchto the intended channel, if prior to channel switching both source anddestination STAs 10 agreed to a channel to be used during their datacommunication. In other words, the source and destination STAs 10 shouldpreferably negotiate concerning the channel to be utilized for theupcoming communication beforehand and reach a mutual agreement. Hence,the shared ISM channel is used to exchange control information in theform of RTS, CTS, ATIM, ACK, etc., to let both involved partiesadvertise their desired channel(s). Upon reaching mutual agreement, theparties (STAs 10) switch to the agreed channel simultaneously and starttheir data communication. As a result, by the use of this approach thereis no need for a separate dedicated control channel formanagement/control purposes.

It is thus preferred that both legacy and cognitive STAs 10A share acommon ISM channel for both management and control purposes.Technically, there is no difference between BSSs 12 established bylegacy STAs 10B and the BSSs 12 initially created by cognitive STAs 10A.In addition, legacy STAs 10B should be able to join BSSs 12 formerlyestablished by cognitive STAs 10A, and vice versa. In any situation, andwhether the BSS 12 was initiated either by a cognitive STA 10A or alegacy STA 10B, cognitive radios are the guests to the ISM band. As aresult, they provide additional services to the legacy STAs 10B whichare licensed users in the band. The basic services offered by cognitiveSTAs 10A may include, but are not limited to, network connectivity andpacket forwarding in layer three. On the other hand, it is preferredthat cognitive STAs 10A are only allowed to use common ISM channel toestablish their connection and reach agreement concerning the channel tobe utilized for their data communication.

Information regarding primary user appearance and related issues arehandled using an extended version of the dynamic frequency selection(DFS) scheme proposed in IEEE 802.11 h. By combining the existing DFSscheme with a number of new concepts, a novel extension to DFS isprovided that is capable of addressing problems related to primary userappearance in non-ISM channels.

The exemplary embodiments also provide novel approaches to preventingundesired congestion in non-ISM channels. Also, by proposing anotherclass of concepts, channel aggregation/bursting in multi-channelscenarios becomes possible, resulting in an enhancement in channelutilization.

In the ensuing description channel identification approaches aredescribed that are suitable for use in broadband cognitive wirelesslocal area networks, followed by a description of an enhanced mediumaccess control protocol for cognitive wireless LANs.

Channel Identification Approaches

When two cognitive STAs 10A desire to communicate with one another theyshould reach a reciprocal conformation concerning the non-ISM channel tobe utilized during their data communication. As explained above thecommon ISM channel, in which the BSS 12 has been formed, is particularlyused for connection establishment and control frame exchange. Duringthis phase, both source and destination STAs 10 should negotiateregarding their desired non-ISM channels to be occupied for the wholedata exchange. However, the way in which STAs 10 advertise theirintended channels is preferably dealt with explicitly. While cognitiveSTAs 10A may be mandated to use common approaches when advertisingdesired channels, this can be done in several ways.

One simple way to advertise intended channels is to mention theirchannel identifiers (CIs) within exchanged control frames (e.g., RTS,CTS, etc.). However, there is no globally unique and wholly acceptedchannel-numbering scheme. For example, in IEEE 802.11a the currentchannel numbering scheme (Channel Identifiers) are as shown in FIG. 2A,while FIG. 2B shows the channel numbering case of IEEE 802.11b and IEEE802.11g, 2.4 GHz band, while FIG. 2C shows the channel numbering schemeof the IEEE 802.11y 3 GHz band.

As should be evident, there is no global agreement as to how differentcenter frequencies are numbered and, as a result, inclusion of thecenter frequency of an advertised channel is preferred as well, and theinclusion of a “channel identifier” for preferred non-ISM channel(s) isnot necessary.

In IEEE 802.11y, in addition to channel center frequency, thecorresponding regulatory class is also defined. Basically, theregulatory class determines several physical layer transmissionspecifications, including channel starting frequency, channel spacing,channel set, transmission power limit, emissions limits set, etc. As aresult, in addition to center frequency, it would be desirable toinclude the regulatory class when advertising intended channel(s). Inaddition, the inclusion of the regulatory class when advertisingintended channel(s) is preferable to only mentioning the targetedchannel bandwidth. Further in this regard, in the future not onlyconventional channel bandwidths, e.g., 5, 10, and 20 MHz, will beavailable, but also other channel bandwidths may be allowed byregulatory authorities. Therefore, a channel bandwidth field may also beincluded within control frames during the channel negotiation phase. Asa result, in addition to the channel center frequency the inclusion ofboth a regulatory class field and a channel bandwidth field aredesirable.

Primary User Detection

There is no major problem presented by Primary User Appearance in thecommon ISM channel shared by legacy and cognitive STAs 10A. This due atleast to the fact that IEEE 802.11-based systems are licensed in thesefrequency bands, and as a result, spectrum sensing for primary userdetection in ISM bands is not mandatory, except for the case of IEEE802.11a (which should be aware of radar signals). Therefore, in a BSS 12comprising both legacy and cognitive STAs 10A, if the shared ISM channelis in the 5 GHz band, all associated STAs 10, including legacy andcognitive STAs 10A, should cooperate in the dynamic frequency selection(DFS) procedure. On the other hand, for all discovered non-ISM frequencyopportunities that may be utilized by cognitive STAs 10A it is preferredthat there be regular (and possibly randomized) spectrum sensingactivities to assure very limited interference to primary users of thisspectrum. Those non-ISM channels in which the primary user is detectedare preferably recorded accordingly by all involving STAs 10. Inaddition, it is desirable that there be a set of counters for everychannel in which primary user has been detected to prevent the MACentity 26 from acquiring forbidden channels. The manner by whichcognitive STAs 10A cooperate in spectrum sensing may be based on anextended version of the IEEE 802.11h DFS scheme. The consideredmodulation scheme to be implemented in the physical layer is based onorthogonal frequency division multiplexing (OFDM). As a result, anynon-decodable signaling in non-ISM channels may be considered as aPrimary User Appearance indication. Basically, if clear channelassessment (CCA), which is a combination of carrier sensing (CS) andenergy detection (ED), detects any type of known Clause 19synchronization (sync) symbols, including Barker code sync and OFDM syncsymbols, it can be concluded that the detected carrier is due to alegacy/cognitive IEEE 802.11 STA 10; otherwise, it may be concluded thatthe detected carrier is due to a primary user and subsequently theoccupied non-ISM channel is released. In general, the cognitive STAs 10Aperform spectrum sensing in at least two different ways: a randomizedapproach and a regular approach.

Frame Exchange Structure for the Cognitive MAC

In order to advertise a certain channel to be used during datacommunication between a pair of STAs 10 the MAC entity 26, depending onthe current situation, may send an ATIM/RTS/Negative non-NullCTS/Negative non-Null ACK frame to its intended STA MAC entity 26.

More specifically, the Announcement Traffic Indication Message (ATIM) isused to inform the recipient about any pending MSDU addressed to itduring a so-called ATIM window just after Beacon frame transmission.Upon reception of an ATIM, the recipient responds with an ACK frame ifit agrees to receive the buffered MSDU(s). On the other hand, if theintended recipient has left the IBSS, there will be no respond and as aresult, the buffered MSDU(s), after expiration of buffering timeout, arediscarded. Basically, ATIM/ACK is used when a power saving (PS) mode isenabled in an IBSS (or BSS). Here, in the cognitive MAC protocol ofinterest to these exemplary embodiments, an ATIM frame may have thefollowing frame formats as its subsequent response:

regular ACK (when the recipient is a legacy STA, it replies the receivedATIM frame using a conventional ACK frame, as in IEEE 802.11),

cognitive Positive ACK (when the recipient is a cognitive STA 10A, andif it agrees with at least one of the offered/advertised channels, itresponds with the Positive ACK),

cognitive Negative Null ACK (when the recipient is a cognitive STA, andif the recipient disagrees with all offered/advertised channels and hasno suggestion to offer, it responds with the Negative Null ACK), and

cognitive Negative non-Null ACK (when the recipient is a cognitive STA,and if it disagrees with all offered/advertised channels and has abetter suggestion(s) to offer, it responds with the Negative Null ACKthat includes its suggestion(s)).

In the latter case the source STA 10 may respond using the Positive orthe Negative Null ACK.

The Ready-To-Send (RTS) is used to inform the recipient about anypending MSDU addressed to it. In the cognitive MAC entity 26 protocol inaccordance with these exemplary embodiments an RTS frame can have thefollowing frame formats as its subsequent response:

regular CTS (when the recipient is a legacy STA 10B, it replies to thereceived RTS frame using a conventional ACK frame, as in IEEE 802.11),

cognitive Positive ACK (when the recipient is a cognitive STA 10A, andif it agrees with at least one of the offered/advertised channels, itresponds with a Positive CTS),

cognitive Negative Null CTS (when the recipient is a cognitive STA 10A,and if it disagrees with all offered/advertised channels while having nochannel suggestion of its own to offer, it responds with a Negative NullCTS), or

cognitive Negative non-Null CTS (when the recipient is a cognitive STA10A, and if it disagrees with all offered/advertised channels whilehaving a (better) channel suggestion(s) to offer, it responds with aNegative non-Null CTS, and places its suggestion(s) within the Negativenon-Null CTS). In this case, the source STA may respond using thePositive or Negative Null ACK).

After performing the regular DCF access procedure (for the case of ATIMand RTS) the source STA 10 may transmit an ATIM/RTS frame to theintended destination STA. The size of the transmitted ATIM/RTS frame ispreferably considered to be variable since it is not clear how manychannels are going to be advertised to the intended receiver. Thetransmitted ATIM/RTS has the following fields: Frame Control (2 Bytes),Duration/ID (2 Bytes), Receiver Address (6 Bytes), Transmitter Address(6 Bytes), BSSID (Basic Service Set ID) (6 Bytes), Sequence Control (2Bytes) (Only for ATIM), Frame Check Sequence (FCS) (4 Bytes), andfinally a variable size Channel Information (CI) field. FIG. 3 shows theposition of the Channel Information (CI) field in control frames, whileFIG. 4 shows a generic Format of Channel Information (CI) Field.

In FIG. 4 the Center Frequency (CF) field (2 Bytes) is specified in MHz,the Regulatory Class (RC) field (1 Byte) is considered mandatory; and ifnot used is loaded with some default value, such as 00 hex; and theChannel Mask field (in particular circumstances Bandwidth (BW)) (1 Byte)which, if the RC field is not used, is set to the recommended bandwidth;5, 10, or 20 MHz (e.g. 5 MHz is represented by 05H or 00000101B). Notethat other values may be used depending on the allowed channelbandwidths. Note also that BW information may be included in the RCfield, as most regulatory classes define the bandwidth of the intendedchannel, in addition to allowed EIRP, etc. Therefore, when the RC fieldis used, it explicitly determines the bandwidth, EIRP (e.g. TransmitPower Limit in mW/MHz), etc. and as a result, BW field may not beneeded. This implies that the RC is a mandatory field while BW isnon-compulsory. On the other hand, when the RC field is not used (loadedby 00H), then BW field is used in order to determine the bandwidth of anegotiated data channel.

The Channel Control (CC) (1 Byte) field in FIG. 4 has the followingsub-fields (reference is made to FIG. 5).

1) A Channel Preference Number (CPN) (2 Bits) which is used to numberoffered channels: 01, 10, or 11 (00 may be reserved and is not used).Upon returning the evaluation results of an offered channel, the CPNsub-field should have the same number as it had when the channel wasbeing advertised.

2) A Proposition/Evaluation Bit (1 Bit) which is used to determinewhether the channel with a preference number included in the CPNsub-field is a channel being advertised for the first time, or a channelwhich has been previously offered and subsequently evaluated by theother MAC entity 26, where Proposition=0 (the channel is beingadvertised), Evaluation=1 (the channel evaluation results are beingdisclosed).

3) A Decision Bit (1 Bit) which is used when the Proposition/EvaluationBit is 1. In this case the Decision Bit determines whether the offeredchannel has been accepted or rejected: Accept=1, Reject=0 (whenProposition/Evaluation=0 this bit is simply ignored, and by default maybe set to 0).

4) Reserved (1 Bit)

5) A Reason Code (3 Bits) which when offering a channel(Proposition/Evaluation Bit=0) specifies the reason for which thechannel is being advertised, as indicated in FIG. 6 (only 000, 001, 010,011); on the other hand, when Proposition/Evaluation Bit=1 thissub-field specifies the reason for which the channel has been accepted(only 010, 011)/rejected (only 000, 001, 100, 101, 110, 111). Note thatthe Decision Bit may be combined with the Reason Code according to theaforementioned definitions.

Note that in an ATIM/RTS (traffic initiator) control frame, there is noneed to determine the duration of intended channel deployment. Upon anyconformity, both source and destination STAs 10 switch to the agreedchannel and, consequently, they exchange regular RTS/CTS to reserve thechannel for a particular time duration.

Also, the following points should be noted. First, only one of theadvertised channels might be selected at any step of the channelnegotiation phase. Second, the source (and destination) STA 10 ispreferably limited in the number of advertised channels. As an example,by default the maximum number of advertised channels may be three (3).If the source STA 10 has more than three candidate channels it selectsthe best three. On the other hand, if the source STA 10 has less thanthree channels to advertise it may present the information of only theavailable channels.

Referring generally to FIG. 7, when a cognitive STA 10A wants to inviteits intended destination STA to establish a connection, it uses an ATIMor a RTS frame and puts its desired non-ISM channel(s) within the CIfield (see FIGS. 3-5). Note that due to a desire to maintain backwardscompatibility it is preferred to use legacy RTS, CTS, ATIM, and ACKframes to enable legacy STAs 10B to receive and recognize the capturedframes. If the destination STA 10 agrees with one of the advertisedchannels, it will respond with a Positive ACK or Positive CTS frame (orsimply with an ACK/CTS frame with an extra CI field as its payload). Onthe other hand, when the destination STA 10 disagrees with the offeredchannels, and has its own suggestions, it responds with a Negativenon-Null ACK or Negative non-Null CTS. When the receiver (thedestination STA 10 in this case) disagrees with the advertised channels,and has no channels at hand to offer, it responds with a Negative NullACK or Negative Null CTS. In this case, no connection with the intendedSTA 10 is established and, later, the source STA 10 may retry withanother possible channel or channels. The manner in which STAs 10 offerthe channel(s) and accept/reject particular channels is based on thefollowing rules.

A. When a certain channel is being advertised, the promoting STA 10assigns a preference number to the channel and places it in the ChannelPreference Number (CPN) field (see FIG. 5). When the recipient STA 10evaluates the channel(s) and reports the evaluation results, it uses thesame number as the channel(s) had when advertised.

B. When a channel is being advertised, the correspondingProposition/Evaluation Bit is set to 0 (Proposition), and when itsevaluation result is being reported the Proposition/Evaluation Bit isset to 1 (Evaluation). For a candidate channel being advertised, theDecision Bit is simply ignored (and may be set to 0). In addition, whena channel is being offered, its physical specifications (e.g., itsregulatory class, center frequency, bandwidth, etc.) are indicated inthe Channel Information (CI) field. The CC field of a particular channelwhich is being advertised is followed immediately by its correspondingCI field. Accordingly, the MAC entity 26 checks theProposition/Evaluation Bit and if it is 0 (Proposition), it expects a CIfield to follow the CC field. On the other hand, in a CC field beinganalyzed, when the Proposition/Evaluation Bit is set to 1, the MACentity 26 expects to find the evaluation report of the channel with thepreference number indicated in the CPN field in the following DecisionBit. If the Decision Bit is 0, the MAC entity 26 can assume that thechannel was rejected by the recipient, and if it is 1, then the MACentity 26 may conclude that the channel has been accepted. In the caseof channel evaluation reporting, the MAC entity 26 does not expect a CIfield to follow the CC field being processed. By the use of thisprocedure and rule set there is no need to include additional header(s)to express the number of advertised/reported channels and so forth.

FIG. 8 illustrates Channel Control (CC) inclusion within the exchangedcontrol frames.

Upon transmission of an ATIM/RTS frame (in cognitive format), theintended receiver analyzes the included fields to deduce all requiredinformation. Here, at least two distinct scenarios are possible.

First, the receiver (intended destination STA) is not a cognitive radio.In this case, it fetches the related information by the use of onlyknown fields and ignores the remaining field(s) without any furtherprocessing. The receiver responds to the received ATIM frame with aregular ACK. Upon reception of the ACK frame, the source STA concludesthat the intended receiver is a non-cognitive STA and, as a result, ituses the conventional ISM band, in which current IBSS has been alreadyestablished, in order to exchange pending MSDU(s) with the receiver.

In a second scenario the receiver is a cognitive radio. In this casethere are multiple possible scenarios that can occur.

A) When the destination STA agrees with at least one of the offeredchannels, it informs the source STA of its agreement to deploy theintended channel. Note that the receiver chooses only one of the offeredchannels based on its own localized decision making procedures, whichmay be based upon an advanced channel feature measurement or otherperformance criteria. The protocol by which the receiver calculates thechannel performance metrics can be any suitable protocol, and is assumedto be based upon PHY and MAC cooperation. The receiver prepares anACK/CTS frame to convey its agreement about one of the advertisedchannels. The appended CC field within the ACK/CTS frame contains a CPNfield loaded by the preference number of the channel that was presentwhen it was being advertised (01, 10, or 11, where 00 may be reservedand not used), Proposition/Evaluation Bit set to 1 (Evaluation),Decision Bit set to 1 (Accepted), Reserved Bit, and Reason Code set toone of the two possibilities, 010 or 011.

B) When the receiver disagrees with the offered channels, and has nosuggestion regarding the channel deployment, it sends the Negative NullACK/Negative Null CTS frame back to the source STA. The appended CCfield within the Negative Null ACK/Negative Null CTS frame contains theCPN field loaded by the preference number of the channel that waspresent when it was being advertised (01, 10, or 11, where 00 may bereserved and not used), Proposition/Evaluation Bit set to 1(Evaluation), Decision Bit set to 0 (Rejected), Reserved Bit, and ReasonCode set to one of four possibilities, 100, 101, 110, or 111.

C) When the receiver disagrees with the offered channels, and has atleast one other suggestion, it advertises its own channels just as thesource STA advertised its channels. In this case then the receiver sendsback a Negative non-Null ACK/Negative non-Null CTS frame with thefollowing fields: a set of CC fields corresponding to the rejectedchannel(s), and a set of CC fields related to the channels beingadvertised accompanied with their CI fields. For the first set, theProposition/Evaluation Bit is set to 1 while for the second set this bitis set to 0. The MAC entity 26, by the use of this bit, is able toreadily determine whether any CI field occurs immediately following a CCfield. Also, for the rejected channels, the Reason Code may be set toone of six possibilities, 000, 001, 100, 101, 110, or 111. Uponreception of the Negative non-Null ACK/Negative non-Null CTS frame, atleast two different operational modes can ensue.

In a first mode, if the source STA disagrees with the offered channels,it will send a Negative Null ACK frame with a sufficient number of CCfield(s) equivalent to the channels advertised by the destination STA.In this case all Proposition/Evaluation Bits in all aforementionedfields should be 1 (Evaluation), while the Decision Bits are set to 0(Rejected). Due to the fact that all Proposition/Evaluation Bits are 1,there will be no CI field.(since nothing is being advertised).

In a second mode, if the source STA agrees with at least one of theoffered channels, it will inform the destination STA of its agreement todeploy the intended channel. In this case the source STA prepares an ACKframe to convey its agreement concerning one of the advertised channels.The appended fields are the CC fields corresponding to the rejectedchannels, with Reason Code sub-fields set appropriately, and a single CCfield that carries a CPN of the accepted channel.

A discussion is now made of MAC entity 26 basic functionality.

It is first noted that there are numerous operational cases that mayoccur during the deployment of a cognitive wireless network that tend tomake the MAC entity 26 more complex than a legacy/regular single channelMAC protocol (e.g., IEEE 802.11 MAC).

In general, designing a MAC algorithm for a cognitive multi-channelsystem may take into account how many transceiver(s) are available forthe designer at the PHY level. In addition, different scenarios exist inthe PS and non-PS modes which should be investigated in detail andaddressed separately. One can categorize different cases according todiverse differentiation criteria. The number of available transceiver(s)is one of the key classification criterions. In addition, as mentionedabove being in PS mode (PS enabled) or non-PS mode (PS disabled) isanother complicating factor. Here, and for simplicity, it is preferredto categorize the possible scenarios according to the number ofavailable transceivers in the physical layer. First there is consideredthe case where the cognitive STA is equipped with two independenttransceivers, followed by the more complex case in which the PHY hasonly one transceiver available for “over the air” activities.

Dual-transceiver Mode-PS Mode Disabled

In this case the cognitive STAs have two independent transceivers whenassociated with a PS disabled Basic Service Set (BSS). In this case ageneral rule is that each STA establishes one of its transceivers on theshared common ISM channel in which the BSS has been established. As aresult, this feature aids the cognitive STAs to more efficiently performchannel sensing processes. On the other hand, in dual-transceiversystems, the amount of power consumption is greater than in asingle-transceiver embodiment.

Beacon frames are assumed to be always transmitted by the transceivertuned on the common ISM channel. In addition, managing the RTS/CTSexchange is performed using this transceiver as well. For simplicity,one may refer to the transceiver tuned to the ISM common channel as theISM transceiver 20, while the other (second) transceiver, which may beat any frequency band to coordinate information exchange betweencognitive STAs, may be referred to as the cognitive transceiver 22 (seeFIG. 1B).

The ISM transceiver 20 is responsible for RTS/CTS frames exchange, andthe coordination between cognitive and non-cognitive STAs. When for thefirst time a tagged cognitive STA (a “tagged” cognitive STA is assumedherein to be a considered STA to which the current focus has beenconcentrated) desires to establish a connection with another associatedSTA in the same BSS, it sends an RTS frame (comprising the extra fieldsintroduced previously) to its intended destination. When the receivedCTS frame corresponding to the delivered RTS implies that the intendedreceiver is a non-cognitive legacy STA, the data exchange is performedin the ISM band. In this case, as there is no possibility forestablishing a further connection to (with) the tagged STA, for powerefficiency reasons the cognitive transceiver 22 may be turned off (ifnot currently involved in any spectrum sensing task). In addition, theabove case is valid when the tagged STA is receiving MSDU(s) fromanother non-cognitive STA in the common ISM band. Here, again,establishing a connection to (with) the tagged STA (another STA) is notpossible since the ISM channel has been already utilized. On the otherhand, when the received CTS frame implies that the intended receiver isa cognitive STA, the two STAs (i.e., the cognitive source STA and thecognitive destination STA) can reach a reciprocal agreement concerningthe data channel to be used for their information exchange. In this casethe cognitive transceiver 22 is tuned to the agreed upon channel tocommence the exchange of RTS/CTS frames.

Assume a case where the tagged cognitive STA is performing datacommunication with another cognitive STA in a non-ISM channel using thecognitive transceiver 22. Now also assume the case where another STAwants to establish a connection with the tagged cognitive STA. In thiscase, when the calling STA is a non-cognitive STA, the consequent datacommunication needs to be done over the shared ISM channel, and therewill be no possibility for other STAs to establish a connection with thetagged STA. On the other hand, when the calling STA is a cognitive STA,the concept of non-ISM Band Convergence applies. In this concept, when adual-transceiver cognitive STA receives a data exchange request in theform of an RTS frame from another cognitive STA, while at the same timebeing involved with another communication in a non-ISM channel, it isrecommended to invite the calling STA to also join the utilized non-ISMchannel being utilized for the ongoing data communication. In such casesthe Reason Code is used to convey the tagged STAs intent to the callingcognitive STA. By using the aforementioned code, the calling STA isenabled to determine why the called (and tagged STA in the aboveexample) is inviting it to switch to a certain channel. Generally inthis scenario, the calling STA advertises up to three channels that maynot be the same as those the tagged STAs is interested in. For thisreason the tagged STA is allowed to reject the offered up to threeadvertised channels and to advertise another channel instead. Toencourage/force the calling STA to select the tagged STAs desiredchannel it may include only its intended channel when it sends aNegative non-Null CTS back to the calling STA.

As another use case, consider a cognitive STA that is communicating withone of its cognitive counterparts in a non-ISM channel. In addition,consider the scenario when the tagged STA also wishes to establish anadditional connection with another STA, in parallel with the ongoingcommunication. The tagged STA uses the ISM channel to send an invitationmessage in the form of an RTS frame to the intended destination STA.When the called STA is not a cognitive STA, the intended data exchangeis performed in the ISM channel. On the other hand, when the called STAis a cognitive STA, the communication may be accomplished using anyknown non-ISM channel. As above, the concept of non-ISM Band Convergencecan be used, where the tagged STA places its desired (already deployed)non-ISM channel in the RTS frame to invite the called STA to join. Toencourage/force the called STA to choose the intended channel, taggedSTA may advertise only the aforementioned channel in order to limit theavailable options of the called STA. In addition, the Reason Code is setto convey the reasoning for the advertisement of the non-ISM channel. Byreception of the RTS the called STA can determine why the tagged STA ispromoting this particular non-ISM channel.

Note that for both aforesaid cases, it is possible for the third party(i.e., the called STA) to reject the tagged STA's offer using theNegative Null control frames (in the first case, using Negative Null ACKand in the second case, using Negative Null/non-Null CTS). In this eventthe third party should disclose its reasoning regarding the rejection ofthe offer of the tagged STA. Using cognitive reasoning, the STAs areable to not only negotiate with one another concerning channeldeployment, but may also obtain valuable information concerning theirsurrounding environment.

Dual-transceiver Mode-PS Mode Enabled

In this scenario the same definitions regarding the ISM and cognitivetransceivers 20, 22 are applicable, while assuming that the cognitiveSTA has two independent transceivers when associated to a PS-enabledBSS. Basically, in a PS mode enabled network, STAs contend with eachother during ATIM window to inform their intended receivers about anypending MSDUs.

In a PS mode enabled BSS, during each ATIM window, those STAs that havepending MSDU(s) for associated STAs send out ATIM frames to informtargeted STAs of the presence of buffered MSDU(s) destined for them.Subsequently, during the remaining time portion of the Beacon Intervalthe buffered MSDU(s) are exchanged.

When the STA has pending MSDU(s) for more than one STA in the same BSS,it is allowed to contend for the shared wireless medium as many times asit intends to send ATIM frames to inform targeted STAs about theexistence of buffered MSDU(s); hence, if the STA is able to contact alltargeted STAs in a single ATIM window, there will be a list of allpending tasks to be accomplished during the remaining time of the BeaconInterval. In other words, cognitive STAs are equipped by a “Task List”24 in which successive tasks (i.e., acting as either source ordestination STA in different channels) are listed according to theirappearance order and, more importantly, their priority relative to eachother. In this context the words and phrase “Task”, “Duty” and “UpcomingJob” may be used to convey the same meaning.

It can be noted that for the dual transceiver mode, each transceiver 20,22 may have its own associated Task List 24A, 24B, meaning that thecognitive transceiver 22 has a dedicated Task List 24A used only for theduties related to non-ISM channels, while the ISM transceiver 20 has adedicated Task List 24B for those duties that may use the shared ISMchannel. For the single transceiver mode all ISM and non-ISM relatedtasks (i.e., cognitive and non-cognitive tasks) are maintained in thesame (unified) Task List. 24.

Within a Task List 24 the task with the highest priority/position ishandled before any other existing/accumulated task. For example, in FIG.9 there is a “Reception (1) C₀“task meaning that upon completion of thecurrent ATIM window the tagged STA is to switch to channel C₀ to waitfor a calling STA willing to send pending MSDU(s) addressed to it. Inthis case “(1)” means that there is only one reception task to beperformed in channel C₀. Note that since the tagged STA knows who willsend pending MSDU(s), upon reception of intended frames from the knowncalling STA it simply knows that it should then switch to the next task.In other words, it is preferred that the tagged STA is not allowed toswitch to the next task before completion of an ongoing task.

Continuing with the simple example shown in FIG. 9, as the secondhighest priority task the tagged STA switches to channel C₁ to send aset of pending MSDU(s) to a waiting STA. This task is shown as“Transmission (1) C₁” meaning that there is only one transmission taskto be done in channel C₁. At the completion of the second task, the STAswitches to channel C₂ to send pending MSDU(s) to another STA. Thisthird task is shown as “Transmission (1) C₂”, meaning that in channel C₂there is only one transmission task recorded for the tagged STA.

As it can be seen from this non-limiting example the task “Reception (1)C₀” has the highest priority among all of the listed tasks shown in FIG.9. In general, “Reception” tasks have a higher priority than“Transmission” tasks due to the fact that “Transmission” can beperformed at any time during a Beacon Interval, while “Reception”mandates that the STA switch to the agreed upon channel and wait for thesource STA to complete pending MSDU(s) reception. As a result, during anATIM window, if the cognitive STA is being elected as a receiving STA ina particular non-ISM channel the “Reception” task is recorded in thenon-ISM (i.e., cognitive) Task List 24A as a duty to be performed withthe highest priority, if there is no other high priority “Reception”task(s) in the Task List 24A.

If there is an existing “Reception” task in the Task List, the new“Reception” tasks may be simply merged with the existing one. This meansthat the new “Reception” task, if is going to be accepted by the taggedSTA, should be performed in the same channel as the existing “Reception”task. This feature may be referred to as a Channel Convergence Conceptand defined for both ISM and non-ISM channels. There are also othercases for which the same concept can be used to perform multiple tasksin a single ISM/non-ISM channel simultaneously.

As another possible use case, assume that there is an existing“Reception” task within the Task List 24 with a highest priority, whilethe new duty to be added to the Task List 24 is a task of type“Transmission”. The tagged STA prefers to perform the new “Transmission”task in the same channel as the highest priority “Reception” duty. Thisis true at least for the reason that the cognitive STA prefers toaccomplish all “Reception” and “Transmission” tasks in the same channelto achieve higher channel throughput by means of trafficaggregation/bursting, while reducing channel switching energy costs andtime. Thus, the STA may offer the non-ISM channel corresponding to theexisting “Reception” duty to the called STA in order to invite it tojoin the intended channel. Now, if the new “Transmission” task isaccepted by the called STA in the offered non-ISM channel, it can bemerged with the existing “Reception” duty and be accomplished in thesame non-ISM channel. This feature follows the Channel ConvergenceConcept and is defined for both ISM and non-ISM channels. On the otherhand, if the agreed upon channel corresponding to the new “Transmission”task differs from the channel used for the existing “Reception” task,the “Transmission” task is preferably added to the end of Task List 24(i.e., with the lowest priority).

When a tagged STA sends/receives an ATIM frame, it is involved in aninteraction in which both parties (i.e., the tagged STA and the otherparty) are allowed to negotiate concerning their desired channel(s) tobe used during their data communication. When the calling STA begins theinteraction, it provides sufficient reasoning regarding its chosennon-ISM channel(s). This reasoning is done with the help of Task List 24and the pre-defined Reason Codes discussed above. As was explained, eachSTA has a set of tasks listed according to their order of appearance,importance, and priorities. Among all existing tasks, there is a taskwith the highest priority that is to be used by the STA. This task maybe a mixed task, e.g., “Reception (3) C₀” which means that exactly threeMSDU receptions are to be performed in channel C₀ from three differentsource STAs. Using the highest priority task, the calling STA begins theinteraction and includes its own reasoning based on the highest prioritytask within the delivered ATIM frame. On the other side the called STAreceives the ATIM frame and, based on the provided Reason Code withinthe ATIM frame, the called STA reacts appropriately according to a setof pre-defined mandatory rules. These pre-defined rules, on one hand,take essential key points for optimized multiple data communicationsinto account while, on the other hand, prevent both involved partiesfrom acting/reacting in a self-interested only manner. In general, theinteracting parties (involved STAs) are concerned with their highestpriority tasks when offering their intended channels to one another and,based on the existing rules, they reach a mutual agreement concerning adata channel.

Note that if the task with the highest priority is a merged “Reception”task with a “Transmission” duty in the same channel, then preferablyonly the “Reception” task is used for channel negotiation.

The pre-defined rules are now explained in further detail. Recall thatthe interacting parties are concerned with their highest priority taskat hand, and the “winner” in a particular interaction is a STA for whichthe offered channel is accepted by the other STA. Upon determination ofthe winner, there is another set of rules which define how the newassigned task should be recorded in the Task List 24 (i.e., should it bemerged with the existing high priority task or simply added to the listwith the lowest priority).

Consider first the four exemplary modes, shown in FIGS. 10A-10D, whichwill be used below.

Assume that, for the first time, the tagged STA to be informed byanother cognitive STA of a pending MSDU that is to be sent to the taggedSTA. After the channel negotiation phase the STAs reach a mutualagreement to use a non-ISM channel after the completion of the ongoingATIM window. As a second event, consider the case where the tagged STAis once more informed of a pending MSDU by another cognitive STA. Theconcept of the non-ISM Band Convergence should thus be used. The taggedSTA receives an ATIM frame advertising a set of non-ISM channels andpossibly none of the advertised channels are the same as the desiredchannel of the tagged STA (which is in fact the one that has been agreedto previously in the former ATIM channel negotiation phase). In thiscase two different scenarios are possible.

A1. When the Reason Code in the received ATIM frame is 000, the taggedSTA rejects the offered channel in the ATIM frame and sends a Negativenon-Null ACK back to the calling cognitive STA, and offers the channelpreferred by the tagged STA. In this case the calling STA should acceptthe offer by the tagged STA if the advertised non-ISM channel is not inits local Primary User Appearance (PUA) table 30 (discussed below withreference to FIG. 15), and if it has satisfactory spectrum qualityresults. Upon completion of ongoing ATIM window, the calling cognitiveSTA first sends the pending MSDU(s) in its own channel, and thenswitches to the channel of the tagged STA channel and sends the MSDU(s)addressed to the tagged STA (Mode II).

B1. When the Reason Code in the received ATIM frame is 001, the taggedSTA rejects the offer in the ATIM frame and sends a Negative non-NullACK back to the calling cognitive STA, and offers the channel preferredby the tagged STA. In this case the calling STA should accept theoffered channel by the tagged STA if the advertised non-ISM channel isnot in its local PUA table 30, and if it has satisfactory spectrumquality results. Upon completion of ongoing ATIM window, the callingcognitive STA waits for its pending MSDU(s) in its own channel and,after reception of the intended MSDU(s), it switches to the channel ofthe tagged STA and sends the MSDU(s) addressed to the tagged STA (ModeIII).

Assume now that instead of a cognitive STA, a legacy non-cognitive STAinforms the tagged STA about a pending MSDU. Since the tagged STA isequipped with the dual transceiver 20, 22 system, it is able to acceptthis request to let the calling legacy STA send the pending MSDU(s)after completion of the ongoing ATIM window (over the ISM channelassociated with ISM transceiver 20).

Alternatively, again assume that after completion of an ongoing ATIMwindow the tagged STA should be a receiving STA in a non-ISM channel,but subsequently wants to send a pending MSDU to another associated STAin the wireless network. In this case the tagged STA is allowed to sendan ATIM frame to inform the intended receiving STA. However, since priorto any ATIM transmission the tagged STA has no idea whether its intendedreceiver STA is a cognitive STA or a legacy, non-cognitive STA, itpreferably assumes that the receiver is a cognitive STA and puts theformerly agreed upon non-ISM channel in the ATIM frame. In addition, thetagged STA is mandated to set the Reason Code of the ATIM frame to 001.In this case two different scenarios are possible, if one assumes thatthe called STA is a cognitive STA.

A2. When the called cognitive STA was to be a receiving STA in thefollowing Beacon Interval, and the offered channel is not the same asits desired non-ISM channel, it rejects the channel offered by thetagged STA and responds with a Negative non-Null ACK containing its owndesired channel. The tagged STA should then accept the offer if thechannel it is not in its local PUA table 30, and if the offered channelhas satisfactory spectrum quality results. Upon completion of theongoing ATIM window, the tagged STA waits for its pending MSDU(s) in itschannel and, after receiving the intended MSDU(s), it switches to thechannel of the called cognitive STA and sends the pending MSDU(s)addressed to the called STA (Mode III).

B2. When the called cognitive STA was to be a source STA in thefollowing Beacon Interval, and the offered channel is not the same asits desired non-ISM channel, it accepts the channel offered by thetagged STA if it is not in its local PUA table 30, and if it hassatisfactory spectrum quality results. Upon completion of the ongoingATIM window the called STA first switches to the desired channel of thetagged STA and waits to receive its intended MSDU(s), then uponreception of the pending MSDU(s) it switches back to its own desiredchannel and sends the pending MSDU(s) to its intended receiver(s) (ModeIV).

Assume now that instead of a cognitive STA, a legacy non-cognitive STAis informed by the tagged STA about a pending MSDU. Since the tagged STAis equipped with the dual transceiver 20, 22 system, it is able tohandle MSDU delivery after completion of the ongoing ATIM window (overthe ISM channel associated with ISM transceiver 20).

It should be noted that if, for the first time, the tagged STA isinformed by a legacy non-cognitive STA about a pending MSDU, it isallowed to accept any other cognitive/non-cognitive ATIM request withoutany particular limitation. The accepted legacy ATIM requests arecoordinated over the ISM channel by the use of ISM transceiver 20.

Assume now that, as in the first case, the tagged STA intends totransmit a pending MSDU to another STA after completion of the currentATIM window. Also assume that the transmission is going to be made to anon-cognitive STA over the shared ISM channel. This transmission can beaccomplished without confusion with any non-ISM data transmission duringthe upcoming Beacon Interval. At this point, and as the second event,consider the following cases.

A3. In a first case the tagged STA is informed about a pending MSDU byanother cognitive STA. In response, the calling and tagged cognitiveSTAs negotiate to reach a mutual agreement concerning a non-ISM channel,and subsequently the tagged STA cognitive transceiver 22 is tuned to theagreed upon non-ISM channel. Afterwards, if a pending MSDU transmissionrequest in the form of an ATIM frame is received from any othercognitive STA, the concept of non-ISM Band Convergence is utilizedaccording to the rules A1, B1 discussed above. When the tagged STAreceives any other requests from non-cognitive STAs, it simply handlesthem in the ISM channel in a manner similar to the IEEE 802.11 legacy PSmode MAC. However, when the tagged STA desires to send any ATIM frame toany other cognitive STA, the concept of non-ISM Band Convergence isutilized according to the rules A2, B2 discussed above.

B3. Another case is concerned with when the tagged STA is informed abouta pending MSDU by another non-cognitive STA. This is exactly the samesituation as the IEEE 802.11 legacy PS mode MAC, meaning that the STAhandles all requests (all together) in the ISM channel. In meantime,when the tagged STA receives an invitation from a cognitive STA, theformer case is followed.

C3. Another case is concerned with when the tagged STA desires to informanother associated STA about a pending MSDU. Since, at this moment, thetagged STA has not agreed to use any particular non-ISM channel, it isallowed to advertise up to three channels based on its localizeddecision making/reasoning. If the called STA is a non-cognitive STA, itshall respond with an ACK frame and subsequently the transmission willbe performed over the ISM channel. On the other hand, if the called STAis a cognitive STA, the two STAs shall negotiate a non-ISM channel to beused. From this point on, all possible events are addressed according tothe rules A4, B4, A5, B5 discussed below.

Now assume that as the first possible case the tagged STA was alreadysupposed to transmit a pending MSDU to another STA after completion ofthe current ATIM window. Also assume that the aforementionedtransmission is going to be made to a cognitive STA in an agreed uponnon-ISM channel. At this point, and as a second event, consider the casewhere the tagged STA is informed about a pending MSDU by anothercognitive STA. In this case two different scenarios are possible.

A4. When the Reason Code in the received ATIM frame is 000, the taggedSTA accepts the offer if it is not in its local PUA table 30, and it hasobtained satisfactory spectrum quality results. Upon completion ofongoing ATIM window, the tagged STA switches to the offered channel toreceive its pending MSDU(s) from the calling STA, then it comes back toits channel and sends the pending MSDU(s) to its intended receiver(s).This feature enables the calling cognitive STA to enhance channelutilization by using a bursting scheme. On the other hand, when framebursting is not possible the calling STA sends the MSDU(s) of the taggedSTA before any other pending MSDU (Mode I).

B4. When the Reason Code in the received ATIM frame is 001, the taggedSTA accepts the offer if it is not in its local PUA table 30, and if ithas obtained satisfactory spectrum quality results. Upon completion ofthe ongoing ATIM window the tagged STA switches to the offered channelto receive its pending MSDU(s) from the calling STA, and then itswitches back to its channel and sends the pending MSDU(s) to itsintended receiver(s) (Mode IV).

Assume now that instead of a cognitive STA, a legacy non-cognitive STAinforms the tagged STA of a pending MSDU. Since the tagged STA isequipped with the dual-transceiver 20, 22 system, it is able to acceptthis request to let the calling legacy STA send the pending MSDU(s)after completion of the ongoing ATIM window (over the ISM channel)

Alternatively, again assume that after completion of an ongoing ATIMwindow the tagged STA is to be a source STA in an agreed non-ISMchannel, but subsequently it desires to send a pending MSDU to anotherassociated STA in the wireless network. In this case the tagged STA isallowed to send an ATIM frame to inform the intended receiving STA.However, since prior to any ATIM transmission the tagged STA has no ideaas to whether its intended receiver is a cognitive STA, it preferablyassumes that the intended receiver is a cognitive STA and it places theformerly agreed upon non-ISM channel in the ATIM frame. In addition, thetagged STA is also mandated to set the Reason Code of the ATIM frame to001. In this case two different scenarios are possible, if it is assumedthat the called STA is a cognitive STA.

A5. When the called cognitive STA was to be a receiving STA in thefollowing Beacon Interval, and the offered channel is not the same asits desired non-ISM channel, it rejects the offer of the tagged STA andresponds with a Negative non-Null ACK containing its own desiredchannel. The tagged STA accepts the offer if it is not in its local PUAtable 30, and if it has obtained satisfactory spectrum quality results.Upon completion of the ongoing ATIM window, the tagged STA first sendsthe pending MSDU(s) in its own desired channel to its intendedreceiver(s), then it switches to the channel of the called STA channeland sends the pending MSDU(s) to it (Mode II).

B5. When the called cognitive STA was to be a source STA in thefollowing Beacon Interval, and the offered channel is not the same asits desired non-ISM channel, it accepts the offer of the tagged STA ifit is not in its local PUA table 30, and if it has obtained satisfactoryspectrum quality results. Upon completion of the ongoing ATIM window thecalled STA first switches to the desired channel of the tagged STA andwaits for it to send its intended MSDU(s), then upon reception of thepending MSDU(s), it switches back to its own desired channel and sendspending MSDU(s) to its intended receiver(s). This feature enables thetagged STA to enhance channel utilization by using bursting. On theother hand, when frame bursting is not possible, the tagged STA sendsthe MSDU(s) of the called STA before any other pending MSDU (Mode I).

Assume now that instead of a cognitive STA, a legacy non-cognitive STAis informed by the tagged STA of a pending MSDU. Since the tagged STA isequipped with the dual-transceiver 20, 22 system, it handles the MSDUdelivery after completion of the ongoing ATIM window over the ISMchannel and by the use of its ISM transceiver 20.

After determining the winner of interaction (negotiation), both involvedSTAs update their Task Lists 24 appropriately. FIGS. 11 and 12 show howthe new task is added to the Task List 24 according to the differentmodes, explained earlier, and the position of party (whether it was acalling STA, i.e., Side A, or a called STA, i.e., Side B).

Explained now in greater detail is how the above-described rules may beused when merging a new task with the existing Task List 24. Considerthe case when the Task List 24 has a “Reception (1) C₀” at the top(highest priority) of its recorded tasks (FIG. 11). As in the first rowin FIG. 11A, assume that the owner of Task List 24 is invited toparticipate in Mode III as the called STA (i.e., Side B). According tothe rules explained earlier, the tagged STA becomes the winner and as aresult the calling STA accepts its offer, i.e., accepts C₀. This meansthat there will be a new task for the called STA as “Reception”, forwhich the agreed upon channel is exactly the same as the existing highpriority task in the Task List 24. Therefore, the new task can be simplymerged with the existing task (Convergence Concept) and, subsequently,the Task List 24 becomes similar to that illustrated list in FIG. 11. Inthe third row, since the new task is “Transmission (1) C₁”, it has thelowest priority and as a result is recorded according to its appearanceorder. Hence, as shown in FIG. 11 it is put at the end of the Task List24. On the other hand, in the fourth row, since the new “Transmission”task has exactly the same agreed upon channel as the existing“Reception” task, it is simply merged with it and, consequently, is behandled in parallel with the “Reception (1) C₀” upon completion of theATIM window.

Similarly, FIG. 12 illustrates all possibilities when a “Transmission”task is at the top of the Task List 24.

During the Beacon Interval, when two cognitive STAs desire to establisha layer two connection, they preferably use RTS/CTS frames to negotiatethe channel to be used later for the data exchange. When the intendedreceiver is unreachable for any reason (e.g., it is situated in theradio range of an ongoing large data communication in the calling STA'sadvertised channel), it is allowed to reject the offered channel andadvertise its own suggestion using the Negative non-Null CTS , with theReason Code (see FIG. 6) set to 110. Upon reception of the Negativenon-Null CTS, the source STA checks the Reason Code and is able todetermine the reason for which its desired channel has been rejected bythe receiver. At this point, according to the source STA decision makingit decides whether to accept the channel counteroffer of the receiver.

All Beacon frames are sent simultaneously over the common ISM channelutilized by legacy and cognitive STAs. Beacon frame generation isperformed in a cooperative fashion by all associated cognitive STAs, inthe same manner as it is performed by legacy STAs and as defined in theIEEE 802.11 standard. During Beacon frame delivery all STAs become quietand all information exchange activities are suspended. Cognitive STAsare encouraged to put information about Recently Discovered Channels ingenerated Beacon frames. On the other hand, cognitive STAs are mandatedto put sufficient information concerning those channels in which aPrimary User has been detected (appeared), accompanied by thecorresponding Time Index. It is imperative to note that the encapsulatedinformation regarding the Primary User Appearance is not necessarilybased on local induction (interpretation), but may be obtained from thereceived Beacon, Probe response, or other types of MAC management framescaptured over the air interface. Furthermore, it should be also pointedout that for Recently Discovered Channels there should not be anyaccompanying Time Index within the Beacon or other management frames (inthis case the Probe Response management frame is not used for RecentlyDiscovered Channel announcement). As it will be clarified below, thecognitive STA examines each discovered channel to conclude whether itshould be recorded in local databases. When the cognitive STAexperiences a non-ISM channel successfully, either in the position of asource STA or in the position of a destination STA, the channel isrecorded in a so-called Last Successfully Experienced Channel (LSEC)database (simply LSEC table 32, shown in FIG. 15 and discussed below).Only when cognitive STA's local interpretation implies that utilizationof a particular non-ISM channel provides a minimum level ofsatisfaction, the channel information can be recorded in the local LSECtable 32. Note that currently the defined level of satisfaction coversonly an ability of successful experience, and an acceptable spectrumquality result.

The Time Index is specified in a number of Beacon Intervals elapsedsince an event has taken place.

As was discussed above, the MAC entity 26 uses the LSEC table 32 ofthose channels that have been successfully experienced by the taggedSTA. Each entry of the LSEC table 32 has two fields: the first field isa Channel Identifier (e.g., center frequency, channel number, etc.) andthe second field is its corresponding Time Index (the number of BeaconIntervals that have elapsed since the last successful experience withthe channel by the tagged STA). The Time Index of LSEC entries is amonotonically increasing timer that increments every Beacon Interval.When the tagged STA utilizes one of the recorded channels in the LSECtable 32 successfully, either as a source or a destination end point,the corresponding Time Index is reset to zero. By definition, a recordedchannel in the LSEC table 32 is referred to as an LSEChannel. To keeptrack of the recorded information level of freshness, the Time IndexDomain is divided to two sub-domains (or zones) as depicted in FIG. 13.

The first zone (sub-domain), LSEChannel Forbidden Zone 29A, is typicallyspanned from 0 to M′. When a discovered channel is successfullyexperienced by the tagged STA (either as a source or destination STA),it receives a Time Index equal to zero and is recorded in the LSEC table32. The second zone, LSEChannel Election Zone 29B, is spanned betweenM′+1 and M. As explained earlier, when a previously recorded channel inthe LSEC table 32 is again experienced successfully, its Time Index isreset to zero. Basically, the MAC entity 26 always selects a non-ISMchannel with the greatest Time Index as its desired choice for anupcoming data communication. This feature makes the non-ISM BandDivergence Concept achievable, as it prevents greedy utilization of aparticular non-ISM channel by cognitive STAs after any successfulexperience with the channel. On the other hand, this feature is indeedimperative for the case where a Primary User appears in a certainnon-ISM channel. If all cognitive STAs concentrate on deployment of onlyone non-ISM channel, upon any Primary User Appearance they shouldconcurrently suspend all ongoing information exchanges, resulting insimultaneous and considerable system performance degradation. Ifassociated cognitive STAs are distributed among all available non-ISMchannels (i.e., frequency opportunities), then upon a Primary UserAppearance in a particular channel only a few cognitive STAs willencounter throughput degradation due to traffic exchange suspension.Note that the MAC entity 26 is not allowed to update the LSEC recordTime Index with any type of received information over the air interface.In addition, upon reporting a new LSEChannel, the reporter is preventedfrom inclusion of any Time Index in the management frame (e.g., Beaconframe) carrying the LSEChannel information.

In addition to the LSEC table 32, there is a Primary User Appearance(PUA) table 30 used to keep track of all channels in which a PrimaryUser has been recently detected. When a Primary User is observed in achannel, using an extended version of a Dynamic Frequency Selection(DFS) scheme (refer to IEEE 802.11h amendment), cognitive STAs aremandated to inform their one-hop neighbors about Primary User appearancein that particular channel. All discovered channels, in which PrimaryUser appearance has been reported by either the local MAC entity 26 orneighboring STAs, should be recorded in PUA table (Note that the termsPUA database and PUA table can be used interchangeably). In PUA table,each entry has a Time Index which is a monotonically decreasing timerand decrements every Beacon Interval. When a channel is being recordedin the PUA table 30, its timer is loaded by a pre-defined value (e.g., anetwork operator-defined value) and begins counting down. When the TimeIndex timer reaches zero, the channel identifier is simply removed fromthe PUA table 30. When a Beacon/Probe Response/DFS frame reporting aPrimary User Appearance is received, the cognitive STA checks itsprivate PUA table 30 to verify whether the reported channel has beenalready recorded in its database; if not, it is recorded and itscorresponding Time Index is simply copied from the received frame. Notethat in contrast to the “Recently Discovered Channel” case where thereporter is prohibited from inclusion of the Time Index in the deliveredmanagement frames (e.g., Beacon frame), for the case of “Primary UserAnnouncement” the reporter is mandated to accompany the channel beingreported with its corresponding Time Index. On the other hand, if thePrimary User Appearance has already been recorded in PUA table 30, thecorresponding Time Indexes in the local database and the received reportframe are compared with each other. When the Time Index in PUA table 30is less than the Time Index in the received report frame, the cognitiveSTA updates the Time Index of the channel entry in its local databasewith the Time Index included in the received frame. When the Time Indexin PUA table 30 is greater than the Time Index in the received frame,the cognitive STA simply drops the received information; i.e.:

If (Rcvd_Frame(Channel_Id(Time_Index)) ≦Local_PUA_Table(Channel_Id(Time_Index))) { Drop the information insidethe received frame; } Else {  Local_PUA_Table(Channel_Id(Time_Index)) ← Rcvd_Frame(Channel_Id(Time_Index)); }

When a Primary User is detected in an LSEChannel, the channel should beremoved from the LSEC table. As a result, upon receiving a Primary UserAppearance notification reported either by the local MAC entity 26 or bya neighboring STA, not only the PUA table 30, but also the LSEC table32, should be checked. All dynamic frequency selection (DFS) relatedframes are transmitted over the ISM channel.

Within, for example, the Beacon and Probe Response frames there shouldbe an Information Element dedicated to Primary User Appearancenotification. This field resides in the optional portion of abovementioned management frames. Note that the corresponding Time Index forPrimary User Appearance event should also be included. Thus, the ChannelIdentifier (e.g., center frequency) and Time Index are two mandatorysub-fields that are always included.

Reference can be made to FIG. 14 for showing this information elementfor Primary User Appearance Reporting purposes.

In addition to the LSEC table 32 and the PUA table 30 there is a sectionwithin the MAC entity 26 databases referred to as a Transient Zone 34that is specifically used for channel management purposes (See FIG. 15).All information concerning discovered channels either by the local MACentity 26 or neighboring STAs is gathered within the Transient Zone 34.A newly discovered non-ISM channel is first checked (block 36) to seewhether is already included in the PUA table 30. After checking the PUATable 30, and if the verified channel has not been recorded in the PUAtable 30, the channel information is recorded in a FIFO-based structure38. The FIFO-based structure 38 is actually a FIFO queue, and channelinformation is queued in this structure and fetched according toinclusion order. On the other hand, if the discovered channel is foundin the PUA table 30, it is simply discarded from the Transient Zone 34.

Head-of-line (HOL) channel information is fetched from the TransientZone FIFO-based queue 38 whenever there is no channel in the LSEC table32 with a Time Index situated in the LSEChannel Election Zone 29B (SeeFIG. 13). Basically, as a first choice, the MAC entity 26 is mandated toselect a candidate channel with a largest Time Index situated inLSEChannel Election Zone 29B. When there is no channel with the TimeIndex situated in LSEChannel Election Zone 29B, the MAC entity 26 shouldcheck the Transient Zone 34 for any channel availability. When at leastone available channel is found in the Transient Zone 34, it is used formedium access and data exchange purposes. If the deployed channelresults to a successful data communication, it is recorded in the LSECtable 32 accompanied by a Time Index equal to zero; otherwise, thechannel information is sent back to the FIFO queue 38 as illustrated inFIG. 15. Finally, when there is no channel with a Time Index situated inLSEChannel Election Zone 29B, and the Transient Zone is empty (FIFOQueue 38 is empty), the MAC entity 26 should select a channel with alargest Time Index in the LSEChannel Election Forbidden Zone 29A (orsimply, LSEChannel Forbidden Zone) shown in FIG. 13.

If a channel selected from the LSEC table 32 is utilized for a datacommunication successfully, its corresponding Time Index will be resetto zero and it will be retained in the LSEC table 32. On the other hand,if the aforementioned channel is utilized for an unsuccessful datacommunication, it will be put into the Transient Zone 34 as illustratedin FIG. 15.

If a channel selected from the Transient Zone 34 is utilized for a datacommunication successfully, it will be recorded in the LSEC table 32 andits corresponding Time Index will be set to zero. On the other hand, ifthe abovementioned channel is utilized for an unsuccessful datacommunication, it will be returned to the Transient Zone 34 as shown inFIG. 15.

To select a channel for an upcoming communication the MAC entity 26first inspects the LSEC table 32 to determine whether a channel with alargest Time Index situated in LSEChannel Election Zone 29B can befound. When there is at least one such channel, it is selected to beadvertized during the channel negotiation phase. Otherwise, the MACentity 26 inspects the Transient Zone 34 and determines if channelinformation exists in the FIFO queue 38; if at least one channel isfound, it is selected. If not, the MAC entity 26 reverts to the LSECtable 32 and determines if any channel with a largest Time Indexsituated in LSEChannel Forbidden Zone 29A. To review, first the LSECtable 32 is checked for any available channel with the largest TimeIndex situated in the LSEChannel Election Zone 29B , then the TransientZone is checked, and finally if the MAC entity 26 needs to chooseadditional channel(s) it checks the LSEC table 32 for any availablechannel with a largest Time Index in LSEChannel Forbidden Zone 29A.

The aforementioned structure makes the use of the non-ISM BandDivergence Concept possible by preventing greedy utilization of aparticular non-ISM channel by cognitive STAs after a successfulexperience with the channel. In other words, the MAC entity 26 operatesto avoid accumulated channel requests for a certain non-ISM channel.Generally, when a successfully experienced channel is time indexed byzero, the MAC entity 26 is prohibited from deploying it again and, as aresult, it becomes available for use by other neighboring STAs. The useof this approach results in reduced channel congestion levels and to areduced backoff delay for highly populated wireless networks. As wasnoted above, the use of this approach is also important for the casewhere the Primary User appears in a certain non-ISM channel. If allassociated cognitive STAs 10A have already concentrated in only onenon-ISM channel, then upon a Primary User Appearance in this particularchannel all STAs 10 would have been mandated to concurrently suspend allongoing information exchanges. In contradistinction, if the cognitiveSTAs 10A have been distributed amongst all available non-ISM channels(frequency opportunities), then upon Primary User Appearance in aparticular channel only some subset of the set of all cognitive STAswould encounter throughput degradation due to traffic exchangesuspension.

The local MAC entity 26 is preferably capable of discovering newfrequency opportunities in a continuous fashion. In addition, the taggedSTA is able to discover new channels from its neighbors by simplylistening to their exchanged control frames (e.g.,ATIM/RTS/CTS/ACK/Negative non-Null CTS/Negative non-Null ACK). By usingthis strategy the STAs 10 share their findings in a cooperative andreactive manner.

As was explained previously, the cognitive STAs 10A are mandated toutilize the ISM channel for BSS establishment, management, and controlinformation exchange. On the other hand, according to the IEEE 802.11standard if a legacy STA 10B receives a management/control frameaccompanied with one of the known Frame Types defined in IEEE 802.11 itprocesses only those fields that it knows how to exploit. This meansthat newly added fields are not processed and will be simply discardedby the legacy STAs 10B. On the other hand, the legacy STAs 10B should beable to process the Duration/ID field and defer from medium accessduring the period when two cognitive STAs 10A are exchanging controlframes. For this reason it is desirable to define how the Duration/IDfield should be set when exchanging control frames over the shared ISMchannel.

The source STA 10 is allowed to advertise up to three channels within anATIM/RTS frame. As a result, generally ATIM/RTS frames have no staticpre-defined size as in legacy IEEE 802.11. Despite the dynamic nature ofthe ATIM/RTS frame size, no complication arises due to the fact that thesource STA 10 may only acquire the control of the medium, andsubsequently is free to transmit its ATIM/RTS without any limitation onthe size of delivered frame. However, at the receiver side a problem mayarise since it may not be clear how the receiver will respond to thereceived ATIM/RTS frame. As a result, the source STA 10 does not knowexactly for how much time it should reserve its surrounding wirelessmedium, using the network allocation vector (NAV) within the ATIM/RTSframe, to enable the called STA to send the expected ACK/CTS frame back.For example, in one case it is possible that one of the offered channelsis accepted by the receiver and, consequently, only CC fields will beincluded within the returned ACK/CTS frame. In this case the source STA10 can readily predict that if the receiver is going to accept theoffer, it will send back three CC fields (one for the accepted channeland two for the rejected channels). However, there may instead be a casewhere the receiver rejects all offered channels, and also advertises upto three channels of its own in the Negative non-Null ACK/Negativenon-Null CTS frame. As should be apparent, in general one may concludethat there is no way for both the source and destination STAs 10 topredict how the other end-point may respond.

To solve this problem it is preferred that the source STA 10 reserve themedium to accommodate a maximum possible returned frame size. As aresult, and in accordance with the exemplary embodiments, the RTSreserves the medium for a CTS frame containing up to three CC fields(the source STA 10 knows exactly how many CC fields will be included ina returned CTS since they exactly correspond to the number of channelspreviously offered in the RTS), in addition to as many as three CIfields (corresponding to the maximum possible three channels that thereceiver is allowed to advertise, if it rejects the three channelsoffered by the source STA 10). As an example, assume that the source STA10 advertises two non-ISM channels, and that the receiver does notaccept the offered channels and prefers instead to advertise only onenon-ISM channel different from those offered by the source STA.According to the aforementioned rule, the source STA reserves itssurrounding area for:

SIFS+legacy_CTSTime+2×CC+3×Cl.

This means that source STA 10, due to its inability to predict how manychannels may be offered by its intended receiver, reserves the mediumfor the case when the receiver offers three different channels.

Related to the dynamic size of the CTS there is a more conservativeapproach, that is, for the receiver limit the allowed number of offeredchannels to one. In this case the source STA is able to anticipate thatif all offered channels are rejected by its intended receiver then therewill be exactly the same number of CC fields as the number of offeredchannels in the RTS, plus one CI field, in the returned CTS frame (i.e.,Negative non-Null CTS). Although in this case the size of returnedNegative non-Null CTS frame is still unpredictable, the incurredvariation is not considerable in comparison to the case in whichreceiver STA is allowed to offer up to three channels. Reconsidering theprevious example, according to the above simplifying rule, the sourceSTA is only required to reserve the channel for:

SIFS+legacy_CTSTime+2×CC+Cl.

On the other hand, if the receiver STA 10 has no channel offer toadvertise, the additional media reservation performed by the source STA10 will be equivalent to one CI, which is only five bytes in size and isthus not a significant portion of the overall reservation.

For the case of the receiver STA, when it reserves its surrounding mediathe situation is simpler. If the receiver STA accepts one of the offeredchannels, it will not need to reserve the media for any additionalperiod. On the other hand, if it rejects all offers and advertises itsown desired channel, it can anticipate an ACK (or Negative ACK) framewith exactly the same number of CC fields as the number of offeredchannels in its Negative non-Null CTS.

As can be appreciated, the media over-reservation potential problemexists only for the source STA 10, and by limiting the number of thereceiver STA possible offers the problem can be at least partlyalleviated.

The following rules are applicable for involved STAs 10 concerningreservation of the wireless medium:

1. ATIM/RTS frame Duration/ID field should be loaded by SIFS+legacy_CTSTime+number of offered channels by source STA×CC+maximum number ofchannels receiver is allowed to advertise if it is going to reject allsource STA's offers×CI (over-reservation is probable).

2. Positive CTS/ACK and Negative Null CTS/ACK frames Duration/ID isloaded by zero since there is no need to reserve the media for extraframe reception.

3. Negative non-Null CTS/ACK frame Duration/ID should be loaded bySIFS+legacy_ACK Time+number of offered channels by receiver×CC (noover-reservation).

Discussed thus far has been the multiple transceiver cognitive STA 10Aembodiment, having the ISM transceiver 20 and the cognitive transceiver22. Discussed now is the single transceiver embodiment.

When the physical layer is equipped with a single transceiver, severalissues arise concerning multi-channel MSDU transmission. In thisdiscussion it may be assumed that the cognitive STAs 10 aresingle-transceiver-based and as a result, each cognitive STA 10A is ableto focus on only one channel, either ISM or non-ISM channel, at anygiven time. Therefore, for example, if the STA 10A is sending orreceiving on a non-ISM channel, then it cannot simultaneously handlelegacy ISM connections. Both the power saving (PS) mode disabled and thePS mode enabled scenarios are covered below.

A) PS Mode Disabled

This mode is similar to the case where the physical layer is equippedwith a dual transceiver (ISM/non-ISM), except that the cognitive STA 10Ais not able to serve any connection establishment request delivered overthe shared ISM channel when it is involved with an ongoing datatransmission on a non-ISM channel. This is due to the fact that the STAhas the single transceiver structure and, thus, it can be tuned to onlyone channel at any given time. As a result the STA which is sending anATIM/RTS frame to establish a connection with a cognitive STA 10A thathas being involved with another data communication in a non-ISM channelwill not receive any response and subsequently will timeout. Theoccurrence of successive timeouts degrades the ISM channel utilizationand wastes available opportunities for other legacy STAs 10B toestablish data communication with their associated counterparts. It canbe assumed that the achieved channel utilization in single-transceivermode is lower than for the case in which the STA is equipped with twoindependent transceivers. Also, it should be noted that theaforementioned throughput degradation is due to the overall structure ofphysical layer, and is not due to the MAC entity 26 itself.

B) PS Mode Enabled

In this case all transmitted/received MSDU(s) delivery requests, in theform of ATIM, are handled exactly as in the dual transceiver mode,except that all ISM and non-ISM related “Transmission” and “Reception”tasks that are to be performed in the upcoming Beacon Interval areaccumulated in a common Task List 24. This means that there is noseparate non-ISM and ISM Task Lists 24A, 24B, due to the fact that asingle transceiver-based STA 10 is capable of handling only one task atany particular time. Therefore, successive tasks are recorded accordingto their appearance order and, more importantly, based on theirpriorities. In conclusion, for the single transceiver case there is onlyone Task List 24 dedicated to both ISM and non-ISM duties.

Concerning the strategic interactions between cognitive STAs 10A duringthe negotiation phase, all of the rules discussed above are applicablewith the following exception.

When there is at least one “non-ISM Reception” task in the (unified)Task List 24, any “ISM Reception” task issued by a legacy STA 10B isrejected. On the other hand, when there is an “ISM Reception” task inthe Task List 24, all other “Reception” tasks are converged to thecommon ISM channel, as the Convergence Concept has been taken intoaccount for all pre-defined interaction rules introduced earlier. Thismay be referred to as ‘ISM Attraction Dilemma’. The ISM AttractionDilemma is undesirable in the sense that it attracts all cognitivetransmissions to the shared common ISM band, which preferably is usedonly for control signaling purposes. Therefore, the “ISM Reception”task(s) are preferably rejected if there is at least one “non-ISMReception” task in the Task List 24. Since legacy STAs 10B are notcapable of switching to non-ISM channels, as a result they are not ableto follow the Convergence Concept in non-ISM channels and, for thisreason, their transmission requests over the ISM channel are simplyrejected (if the cognitive STA 10A has already agreed to a “Reception”task over a non-ISM channel).

FIG. 16 shows a modified Task List maintenance rule and strategy that isbased on the foregoing discussion of the single transceiver embodimentof the STA 10.

As it can be seen in FIG. 16, the ISM Attraction Dilemma is possible forthree different cases. Since the tagged STA has an “ISM Reception” task,as a result all other accepted “Reception” tasks are also attracted tothe ISM channel. For the fourth row, there is also a possibility of ISMAttraction, if the existing “Reception” task in Task List 24 is relatedto a legacy STA 10B.

Based on the foregoing it can be appreciated that a novel cognitivefrequency agile MAC protocol entity 26 has been described, one suitablefor use with, but not limited to, next generation 802.11 wirelessnetworks. The MAC entity 26 is capable of coordination of concurrentmulti-channel data communications in a distributed fashion. Both thepower save mode disabled and power save mode enabled modes areaccommodated while taking into account both single transceiver and dualtransceiver physical layer structures. The MAC entity 26 protocolalgorithm is designed in such a way that it makes both non-ISM channelConvergence and Divergence Concepts simultaneously possible andachievable. The use of these two concepts improves channel utilizationon one hand, and on the other hand prevents congestion, in particular innon-ISM channels. For each of aforementioned concepts novel strategies,including the use of dual-zone timers, strategic decision-making schemesand the Task Lists 24A, 24B, have been described. In addition, it can benoted that the exemplary embodiments do not require any dedicatedcontrol channel structure for the cognitive STAs 10A, while providingadditional services for legacy existing IEEE 802.11 networks. Also, thecognitive MAC entity 26 has complete backwards compatibility with thelegacy IEEE 802.11 MAC, meaning that the legacy STAs 10B are able toreceive and process all MAC frames transmitted by the cognitive STAs10A. As a result, direct communication between a legacy STA 10B and acognitive STA 10A become possible.

Simulations have shown that a channel utilization enhancement of about 6to 7 percent for existing IEEE 802.11 networks becomes possible due atleast to the additional network services offered by cognitive STAs 10A,while achieving high channel throughput in non-ISM channels forcognitive STAs due to better medium access coordination.

Described now are further enhancements to cognitive radio techniques inaccordance with additional embodiments.

In the final version of IEEE 802.11s amendment a so-called commonchannel framework (CCF) is to be considered as a non-compulsorytechnique to offer higher aggregate channel throughput due tosimultaneous multiple channel deployment and concurrent datatransmissions. In this approach mesh points (MPs) are allowed to utilizea common channel to negotiate about an available data channel that willbe deployed for exchanging data frame(s) between the source and thedestination entities (abbreviated by SE and DE). The negotiation phaseis accomplished by exchanging two designated control frames referred toas ready-to-switch (RTX) and clear-to-switch (CTX).

It is noted in this regard that according to the IEEE 802.11s standard,any device that supports pre-defined mesh services in a wireless meshnetwork (WMN) is called a mesh point (MP). Note that a MP can be eithera dedicated infrastructure device or a user appliance that is able tofully participate in both the formation and operation of the meshnetwork simultaneously.

Further in this regard the source entity (SE) refers to any type of meshequipment that has something to send. This can be either a MP or a meshaccess point (MAP). In addition, a cognitive source entity (CSE) may beconsidered to be a frequency agile SE. The destination entity (DE)refers to any type of mesh equipment that is intended to receive dataframe(s) from a SE. Similarly, by cognitive destination entity (CDE)what is intended is a frequency agile DE.

At the beginning of the exchange, the SE sends an RTX frame over thecommon channel to inform the DE of an intended data transmissiontargeted to it. The SE offers an empty channel to the DE which is to bedeployed during the data transmission. Using a dedicated field in theheader of the RTX, i.e., “destination channel information”, the SEadvertises the channel to the DE. When the DE is also interested indeployment of the offered channel, it responds using a CTX control framewhich is also transmitted over the shared common channel. Subsequent tothe correct reception of the CTX frame by the SE, both involved entitiesswitch to the destination channel in order to commence the agreed upondata transmission. After switching to the destination channel, and aftera time period equal to DIFS (Distributed Inter-Frame Space), if themedia is sensed idle the SE will be allowed to start transmission ofdata frame(s) to the DE. At the end, an acknowledgment (ACK) frame isdelivered through the destination channel back to the SE. It is notedthat there is a special type of MP, the mesh access point (MAP), whichserves also as an access point (AP) in addition to providing pre-definedconventional mesh services.

In IEEE 802.11s it is assumed that the MPs are equipped with a singleradio transceiver. As a result, a particular MP on the common channel isunable to communicate with other MPs which are operating on the otherchannels. At the same time, single-radio MPs on other channels areunaware of the network status on the common channel.

As was discussed above, the cognitive IEEE 802.11 STAs 10A are able toestablish the cognitive basic service set (CBSS) to which both legacyand cognitive STAs are able to join. All CBSSs are established on theISM frequency bands in which the legacy STAs 10B operate, enabling alllegacy STAs 10B to detect, probe and associate to the existing CBSSs. Inaddition, based on the above concepts the cognitive STAs 10A are notallowed to deploy the shared ISM channel for private data transmissions,except in the case where a legacy STA 10B wants to establish a linklayer connection with a cognitive STA 10A, or when the destination ofinterest of a cognitive STA 10A is a legacy STA 10B. In these two casesthe cognitive STA 10A operates on the shared ISM channel in order to beable to exchange the intended data frame(s) with the legacy STA 10B. Byestablishing the CBSS over a conventional ISM channel, the cognitiveSTAs 10A are able to provide additional network connectivity and packetforwarding to the legacy system on one hand, and on the other hand theyare allowed to utilize the shared ISM channel as a common controlchannel that is primarily exploited forcognitive-management/cognitive-control traffic transmissions. Based onthe above-referenced cognitive medium access control protocol one mayconclude that there is no need for a common control channel to beparticularly specified in order to enable the cognitive STAs 10A tonegotiate about the use of non-ISM data channels.

The exemplary embodiments extend the foregoing MAC entity protocol andoperation to the IEEE 802.11s type of WMNs. In this case a cognitivewireless mesh network (CWMN) may be defined as a set of mesh entities(MEs) including both cognitive MPs/MAPs and conventional or legacy802.11s MPs/MAPs. In the CWMN ISM band(s)/channel(s) are particularlyutilized for 802.11s MPs/MAPs and legacy 802.11 STAs traffic delivery,and for exchanging cognitive-management and control frames to negotiateconcerning non-ISM channels that may be deployed. In this CWMNarchitecture the ISM band(s)/channel(s) are deployed as common controlchannel by all cognitive STAs, cognitive MPs (CMPs), and cognitive MAPs(CMAPs). As a result, cognitive mesh entities (CMEs) 40 shouldpreferably avoid using ISM bands/channels for private data transmissionsas much as possible. On the other hand, and based on the abovearchitecture, non-ISM channels are specially utilized for datatransmissions in a distributed manner coordinated by cognitive STAs,CMPs, and CMAPs.

As employed herein an ME encompasses any type of mesh equipment thatbelongs to the WMN. This can be a simple IEEE 802.11 STA which has beenalready associated to the WMN, an MP, or an MAP. In addition, an CME isany type of ME that exhibits frequency agility, and may be a cognitive802.11 STA, an CMP, or an CMAP.

FIG. 17 shows a simplified block diagram of a two transceiver CME 40.Similar to the cognitive STA 10A having the cognitive MAC entityprotocol discussed above, each CME 40 is equipped with a plurality oftransceivers, namely an ISM transceiver 42 and a non-ISM (cognitive)transceiver 44. The ISM transceiver 42 is particularly dedicated tooperate on the shared ISM channel(s), while the non-ISM transceiver 44functions as a cognitive transceiver capable of switching betweendifferent non-ISM frequency bands to handle data transmissions in aparallel fashion. One result of this architecture is that the CME 40does not suffer from the problem of not being aware of the networkstatus. Note again in this regard that in IEEE 802.11s it is assumedthat the MPs are equipped with a single radio transceiver. As a resultan MP operating on the common channel is unable to communicate withother MPs which are operating on the other channels. At the same time, asingle radio (single transceiver) MP operating on one of the otherchannels is unaware of the network status on the common channel.

Note that the shared ISM channel is especially dedicated to onlycognitive control and management purposes, and not to data transmissionsconducted by cognitive STAs/CMPs/CMAPs, i.e., CMEs. It is assumed thatthere should be always an available common control channel that issubstantially free of any primary user deployment, so that the cognitiveradios are always allowed and able to utilize it to negotiate about anypossible deployable non-ISM data channel for their private datatransactions. Existing ISM channels may be utilized by eitherindependent neighboring wireless LAN hotspots, IEEE 802.11 STAsassociated with the WMN, or legacy (i.e., non-cognitive) MPs/MAPs. Theresult is the deployment of a CWMN that comprises both cognitive andnon-cognitive MPs/MAPs and various types of legacy IEEE 802.11 entities.The shared ISM channel(s) are set aside particularly for use by legacynon-cognitive 802.11/802.11s equipment.

Further in accordance with the exemplary embodiment, the cognitive MACentity 26 discussed above is incorporated into the CME 40 as the MACentity 46 (see FIG. 17).

FIG. 17, discussed above, shows a non-limiting example of a CME 40. Forthe purposes of describing the exemplary embodiments, a CDE and a CSEmay each be constructed along the lines of the CME 40, as well as alongthe lines of the cognitive STA 10A shown in FIG. 1B, and preferablyinclude the MAC entity 26 that functions as described above. Note thatat one particular time a particular CME 40 may function as a CDE, and atanother time it may function as a CSE.

Of particular interest is the non-compulsory CCF which is expected to beincluded in the final version of 802.11s amendment. FIG. 18 illustratesthe basic concept of CCF.

Regarding the IEEE 802.11s CCF scheme, and as was noted above, both RTXand CTX control frames are transmitted over the common channel. The mainreason for exchanging these two control frames on the common channel isthat mesh entities, e.g. MPs/MAPs, do not have any a priori knowledgeabout deployed and/or preferred data channels of other mesh entities. Asa result, source entities are required to transmit RTX frames over thecommon channel, and the destination entities of interest are expected tobe waiting for a link layer connection establishment request. Thecurrent IEEE 802.11s CCF scheme suffers at least from a lack ofknowledge about the network status when a tagged ME is currentlyoperating on a channel other than the common channel. As a result, thereis no guarantee that a particular RTX will lead to a successful linklayer connection establishment.

The exemplary embodiments not only apply the enhanced cognitive MACentity to the WMN, but also reduce the incurred control overhead due tothe channel negotiation phase. Recalling that in IEEE 802.11s there is aparticular common channel and a few parallel/orthogonal data channelsthat are chiefly dedicated to data transmission, the exemplaryembodiments employ the ISM channel(s)/band(s) as common channel(s),while all available non-ISM frequency opportunities can be utilized fordata transmissions by the CMEs 40.

An important aspect of this feature is the way in which CMEs 40 areconfigured to operate on non-ISM channels in an efficient fashion. Incontrast to the cognitive 802.11 entities that were discussed above,such as the cognitive STAs 10A, it is more efficient for a CME 40 toselect an available non-ISM frequency opportunity, based on a set ofpre-defined spectrum sensing criteria, as its long-term residencychannel (LTRC), and then subsequently inform its one-hop neighbor MEs ofthe selected LTRC. After choosing a particular non-ISM channel as theLTRC, the CME 40 keeps its non-ISM transceiver 44 tuned to the selectedLTRC until, based on some criterion or criteria, it becomes evident thatswitching to another channel may be more beneficial. In the case ofpermanent channel switching, the CME 40 is mandated to announce the newnon-ISM channel that is going to be utilized just after the switchingannouncement. Basically, permanent channel switching is announced usinga designated frame referred to as a channel switching (CHSW) frame.

When the CME 40 wishes to commence a data transmission to one of itsone-hop cognitive mesh neighbors (CMNs), due to the fact that it alreadyknows the LTRC of the intended DE, the negotiation phase can be simplyremoved if the SE is also interested in the current residency channel ofthe DE. To accomplish the intended data transmission, the CME 40switches its cognitive transceiver 44 from its LTRC to the LTRC of theDE. When the CME 40 decides to switch its cognitive transceiver 44 toanother non-ISM channel to conduct a data transmission, it preferablyreports this fact, and the corresponding absence period from its LTRC.

When the CME 40 decides to switch to another channel for a planned datatransmission, it may use an eRTX frame sent over the shared ISM channel.As employed herein the CMEs 40, instead of using RTX/CTX, exchange neweRTX/eCTX control frames. The new eRTX/eCTX frames are similar toconventional RTX/CTX frames, but contain additional fields. Sending theeRTX frame over the shared ISM channel simultaneously achieves twogoals: 1) establishment of a link layer connection with the intended DE,and 2) informing the one-hop neighbors about the absence (on-leave)status (absence from the LTRC) and its corresponding time duration. Notethat the overhead due to CMEs 40 is reduced by the use of only onecontrol frame (the eRTX control frame) to establish the intended linklayer connection and to report the on-leave status for a particular timeperiod.

By the use of these techniques MEs are provided with frequency agilityto obtain higher channel capacity and to coordinate channel activitiesin such a way as to incur lowest level of overhead in the common controlchannel. In addition, on-leave information can be simply employed fordestination non-ISM channel (the LTRC of the DE) reservation purposes,in a manner similar to the Duration/ID which is chiefly used forupdating the network allocation vector (NAV) in 802.11 ISM channels.Here, the legacy IEEE 802.11 (and its 802.11s amendment) Duration/IDfield of the eRTX and eCTX control frames are used for the shared ISMchannel reservation (i.e., NAV update in ISM channel). In contrast, theon-leave information carried by a designated field in eRTX/eCTX is usedfor the destination non-ISM channel reservation in which the targetedcognitive data transmission is intended to be accomplished.

When the a priori knowledge about the CDE current LTRC is correct, uponreception of an eRTX which carries the correct CDE LTRC channelinformation the CDE can simply respond with an eCTX frame. This does notoccur over the shared ISM channel, but instead on the current non-ISMLTRC of the CDE. In addition to eCTX, both DATA and ACK frames arepreferably also sent on the CDE's LTRC. Based on this approach the usageof the shared ISM channel is minimized, as it need be utilized only forcognitive control frame exchange.

On the other hand, when the CSE has incorrect a priori knowledge aboutthe LTRC of the desired CDE, upon reception of the eRTX frame by the CDEit becomes aware that the knowledge of the CSE about its current LTRC isincorrect and, as a consequence, the expected eCTX frame is deliveredover the ISM channel. Afterwards the CSE receives the eCTX from theshared ISM channel and is informed of its incorrect knowledge concerningthe LTRC of the intended CDE. In this circumstance the CDE is expectedto place the correct information in the transmitted eCTX and, in asubsequent step, the CSE sends another eRTX frame over the shared ISMchannel, but with the updated (and now correct) information. It can benoted that reception of an eRTX frame, which carries incorrectinformation, by entities that have no prior background knowledge of theLTRC of the CDE distributes incorrect information through the network.Thus, such undesirable cases are preferably addressed as quickly aspossible. By sending another eRTX frame the CSE prevents distribution ofinconsistent information through the wireless system. The CSE is thenallowed to commence its data transmission over the LTRC of the CDE aftersending the second eRTX, and an additional SIFS.

Another issue that should be addressed properly is the case where a CMEdecides to perform a temporary channel switching operation while atleast one of its neighbors has already initiated backoff cycles intendedfor data transmission to the CME. Recall that the switching entities arerequired to announce their transition to the other channels in the formof eRTX frame if the transition is intended for a data transmission.Upon reception of a switching notification in the form of an eRTX, thecognitive entity or entities that are conducting the backoff cyclespreferably suspend the counting down of backoff timers until the end ofthe on-leave period. In the case of a permanent switching operationthere is no need to suspend the ongoing backoff cycle, since based onthe cognitive scheme, CMEs are enforced to follow two rules whencounting down their backoff counters:

1. If the backoff counter is loaded by an integer value B, for anysubsequent countdowns before reaching ‘1’ CME shall perform carriersensing only on the shared ISM channel;

2. For the last countdown, i.e., when counting down from one to zero,both the shared ISM and the destination non-ISM channels aresimultaneously sensed as being idle for at least a time duration equalto DIFS (i.e., Distributed Inter-Frame Space).

An important difference between the conventional backoff algorithmemployed by IEEE 802.11s and the one described herein leads to a loweraccess delay in comparison to the existing multi-channel MAC protocols.In addition, the backoff technique is more robust to the hidden terminalproblem, as compared to the 802.11s common channel framework.

It can be noted that a WMN may be considered to be substantially fixedin nature (i.e., experiencing little or no topology alteration) and, asa result, the use of distributed radio resource allocation techniquescan be more effective in these kinds of wireless systems as compared toinfrastructure-less mobile ad hoc networks. Although the mesh entitiesdo not exhibit mobility (or at least they are intended to have nomobility during a long-term deployment), the wireless clients associatedwith the WMN are totally free to roam between different 802.11 hotspotsand regional basic service areas (BSAs). Since 802.11s-based meshentities are unaware of the network status when they are operating on achannel other than the common channel, both the multi-hop nature of thewireless system and the client mobility can lead to system throughputdegradation and higher medium access delay. The exemplary embodimentsdescribed below address these various problems in adistributed/frequency-aware manner.

Described now are embodiments of the protocol core algorithm and thecorresponding frame structures. Based on the enhanced MAC entity 26 andrelated features that were described above, the channel information (CI)field is added to the header of control 802.11 frames (e.g.,announcement traffic indication message (ATIM), ready-to-send (RTS),clear-to-send (CTS), etc.) and management 802.11 frames (e.g., Beacon,Probe Response, etc.) and is used for advertising possibly deployablenon-ISM channels. The definition of the position of new header field isimportant so that legacy 802.11 equipment are enabled torecognize/compile all legacy/known header fields to enable, for example,their NAVs to be correctly updated. In other words, the legacy STAs 10Bshould be able to deduce all required information from the legacyfields, and the new fields should be placed in such a way that they canbe simply discarded by the legacy 802.11 STAs. One preferred locationfor the CI field is before the frame check sequence (FCS) field in allcontrol/management frames.

As was noted above, in IEEE 802.11s two designated control frames, i.e.,RTX and CTX, are used by the CCF scheme especially for link layerconnection establishment between neighboring MEs. At least one aspect ofthe disclosed embodiments includes expanding the RTX/CTX framefunctionality to enable the CWMN to coordinate cognitive concurrent datatransmissions in an efficient manner. These control frames are renamedas eRTX and eCTX, respectively (see FIGS. 20A and 20B). Note that byintroducing eRTX/eCTX it is not intended to define any new frame type tothe existing IEEE 802.11s standard. Instead the same frame types as forthe legacy RTX/CTX are used, but with additional fields. When the CME 40desires to set up a link layer connection with another CME using thecognitive common channel framework (CCCF), it sends out an eRTX frameover the shared ISM channel in which the CWMN is already established.There is no need for the CME 40 to advertise any non-ISM channels to theintended CDEs when requesting a link layer connection set up. In fact,each CME 40, based on a set of pre-defined channel sensing criteria,chooses a non-ISM channel as its LTRC and then tunes its non-ISMcognitive transceiver 44 to the selected LTRC. For establishing a linklayer connection with a CME, the CSE switches to the LTRC of the CDE inorder to accomplish the data transmission. For this reason the CSEplaces the channel information of the LTRC of the CDE within the eRTX tobe delivered on the shared ISM channel. The destination channelinformation is included in a designated field, which may be referred toas achannel switching information element (CHSWIE). All one-hopneighbors of the CSE, by reception of the transmitted eRTX, are informedof the time period during which the cognitive neighbor will be on-leave.In fact, the CSE may be mandated to report its on-leave duration sinceif it is assumed that every CME 40 is equipped with only one non-ISMtransceiver 44 that can be tuned to only one channel at a given time. Bytransitioning to another channel the CME 40 is unable to receive anydata frames on its LTRC and, as a result, all CMEs that are interestedin transmitting data frames to the channel switching CME need to beinformed about the situation. For example, a CME 40 that has alreadyinitiated a backoff cycle for data transmission to another CME, which isgoing to switch temporarily from its LTRC to a different channel, shouldbe informed to suspend the ongoing backoff cycle for the duration of theon-leave period. In addition, and as was noted above, the on-leave timeduration is also employed for medium reservation and NAV update in thedestination channel to which the CME desires to switch.

In accordance with this aspect, there are defined two different types ofchannel switching that the CME 40 is allowed to perform. A first type ofchannel switching is referred to as temporary switching, and isaccomplished when the CME 40 wants to perform a data transmission on anon-ISM channel other than its LTRC. The second type of channelswitching is referred to as permanent switching, and is conducted by theCME 40 based on a set of pre-defined channel sensing criteria (e.g., itdiscovers that switching to another non-ISM channel can be morebeneficial). Due to the fact that temporary channel switching is alwaysinitiated by the CSE 40 when it desires to perform a data transmission,the eRTX control frame is used to establish the intended link layerconnection and to also simultaneously inform one-hop CMEs of the channelswitching. Furthermore, the newly defined channel switching (CHSW)control frame is used to report permanent switching.

FIG. 19 illustrates a simple frame flow to announce a permanentswitching of the CME 40 from channel C1 to channel C2. The permanentchannel switching announcement is made using the CHSW transmitted on theshared ISM channel. As the first step, the switching CME 40 initiates abackoff cycle and performs continuous carrier sensing on the shared ISMchannel. When the backoff counter reaches zero, the CME 40 sends out aCHSW frame on the shared ISM channel carrying the information of thenon-ISM channel to which the switching is to be accomplished. Sincethere is no particular destination/receptor entity for the CHSW frame,the receiver address (RA) in the CHSW may be loaded with, for example,the frame initiator MAC address.

In addition to the aforementioned channel switching approaches, whichare basically initiated by the cognitive entity (CE), another type ofpermanent channel switching is one initiated by the CME 40 that desiresto transmit a set of data frames to more than one CDE. In this approachthe CSE invites all of the intended CDEs to congregate in a particularnon-ISM channel to receive the data frames in an integrated manner. Inthis way the CSE achieves a higher transmission capacity since it isable to accomplish all intended data deliveries using frame bursting. Toattain this goal the CSE sends out a designated frame, which may bereferred to as a switching invitation (SWinv) frame, on the shared ISMchannel. The channel capacity improvement based on this technique may bereferred to as welfare enhancement (WE).

It can be noted that this approach may also be employed for link layermulticasting. For the case of multicasting, the multicast MAC address issimply placed in the dedicated RA of the SWinv control frame. However,for the case of WE with multiple unicast data transmissions, multipleunicast MAC addresses are used to invite individual CDEs 40 to switch tothe channel of interest. In the CCCF it is possible to combine unicastand multicast channel switching invitations in a single SWinv controlframe, as explained below.

FIGS. 20A and 20B illustrate the frame structure of the eRTX and eCTX,respectively. Similar to the legacy RTX and CTX control frames definedin IEEE 802.11s, an eRTX/eCTX includes an initial 2 byte frame controland 2 byte Duration/ID fields. With regard to how the Duration/ID fieldshould be set for eRTX and eCTX, in essence the Duration/ID field ofeRTX and eCTX frames is specially used for the shared ISM channelreservation and NAV update. On the other hand, the on-leave durationinformation carried by eRTX/eCTX frames, which reflects the on-leavestatus time duration of the CSE, is used for destination non-ISM channelreservation purposes.

The above-described new CHSWIE field is inserted into both the eRTX andeCTX control frames just before FCS field. For eRTX and eCTX frames theCHSWIE field has a variable length depending on the applicationscenario. In addition, it should be noted that RA in the eRTX frame canbe loaded with either a unicast, a multicast, or a broadcast MACaddress, whereas the same field in the eCTX frame can be loaded onlywith the unicast MAC addresses.

FIG. 21 shows the frame format of CHSW control frame. The CHSW frame isused whenever the CME 40 decides to change its preferred LTRC channelpermanently. The switching CME 40 sends out the CHSW control frame overthe shared ISM channel, with RA field loaded with the MAC address of theCME sending the CHSW control frame. This strategy is somewhat similar tothe ‘CTS to self’ technique defined in the IEEE 802.11g amendment, butwith a different application.

FIG. 22 illustrates the detailed structure of the CHSWIE field used ineRTX, eCTX, and CHSW frames. Up to two CI sub-fields are included in asingle CHSWIE. The CI structure was described above (see FIGS. 3 and 4and the corresponding description of same). The first byte of the CHSWIEis dedicated to channel control (CC) in order to control the basicstructure of the CHSWIE and its contents. In the CC field the firstseveral bits are assigned to convey “CHSWIE status”. Basically, if theCHSWIE has no appended CI sub-field, then the CHSWIE status is set to 00(i.e., Empty CHSWIE); otherwise, the aforementioned bits are loaded with11 (i.e., non-Empty CHSWIE). The next two successive bits in CC (i.e.,the Proposition/Evaluation and Decision Bits) are not currently used inCCCF and, together with the subsequent reserved bit, may be used forfuture protocol development purposes. Note that the bits of the ReasonCode in CCCF have different meanings than those shown in FIG. 22. Thefirst bit, i.e. “Permanent/Temporary Switching Flag”, is used to specifywhether the intended channel switching is permanent or temporary. Thesecond bit, i.e., “No. of Channel Fields”, specifies the number of CIsthat are appended to the CHSWIE. The last bit, i.e., “Application Bit”,may be used in conjunction with the preceding bits.

When there is only one CI within the CHSWIE, as shown in FIG. 22, it maybe used for permanent switching. In this case the CI sub-field carriesthe information of the non-ISM channel to which the permanent switchingby the CME 40 is to occur. Generally, the Regulatory Class, Channel Maskand the channel Center Frequency are the three sub-fields that areincluded in every CI regardless of application or type of switching.When the CME 40 decides to permanently change its current LTRC andswitch to another non-ISM channel, it places the information descriptiveof the new channel within the CI of the CHSWIE appended in a CHSW frame,and sends it over the shared ISM channel (see FIG. 19).

On the other hand when there are two CIs within the CHSWIE, the CHSWIEfield is intended to be used in either eRTX or eCTX (i.e., temporaryswitching). In this case the first CI represents the “other partynon-ISM channel information” while the second CI corresponds to the“local party non-ISM channel information”. By “other party” what ismeant is the CME 40 to which the frame is addressed, i.e., the framereceptor. By “local party” what is meant is the frame initiator that istransmitting the frame over the wireless channel. As an example, for aneRTX frame the “other party” refers to the CDE and the “local party”refers to the CSE that is delivering the eRTX. As another example, foran eCTX frame the “other party” refers to the original CSE that desiresto send data frames to a destination of interest, while the “localparty” refers to the original CDE who is to receive data frames from theCSE.

The CHSWIE is terminated by a two bytes representing the on-leaveduration (OLD) sub-field. The OLD sub-field specifies the time durationof absence of the switching CME from its LTRC. For temporary channelswitching, the OLD sub-field is loaded with a non-zero value between0000 and FFFF (hexadecimal). In contrast, when the CME is performing apermanent switch to another LTRC the OLD sub-field is with FFFF.Basically, the Duration/ID field in both the eRTX and eCTX is employedfor the shared ISM channel reservation and NAV update, while the OLDsub-field of the CHSWIE in eRTX and eCTX is used not only for on-leaveduration reporting, but also for channel reservation and NAV update inthe destination channel (e.g., the LTRC of the CDE). Therefore, it isimportant to define the way by which both the Duration/ID and OLDsub-fields are tuned when exchanging eRTX/eCTX control frames. For thisreason, a consideration is made of all possible scenarios that can takeplace when the CME 40 desires to commence a data transmission withanother CME based on different combinations of Reason Code bit patternand CHSWIE status. The Tables shown in FIGS. 23A and 23B tabulate thesediverse scenarios in an integrated fashion. Note in this regard that themost significant bit (MSB) of the Reason Code field specifies the typeof switching, i.e., Temporary (TSW) or Permanent (PSW). In the case ofTemporary Switching, the second bit determines the number of ChannelInformation (CI) fields located between Channel Control (CC) and theOn-Leave Duration (OLD) field. Possible CI fields are other party andlocal party non-ISM CI. In the case of Temporary Switching, when two CIfields are included (i.e., when the second bit is ‘1’), the other partyCI should be always before the local party CI (i.e., frame initiatorCI). For example, for the case of an eCTX with two CI fields, the firstCI corresponds to the CSE (other party) and the second CI corresponds tothe CDE (local party or eCTX initiator) non-ISM channel information,respectively. Note that in these Tables, in addition to the content ofexisting CI fields (i.e., the carried information), the reason for whichthe CI field is included is also presented, where the content isunderlined and the reason is placed within brackets [ ]. Further, by“CME's channel information” is meant “the CME's current non-ISM channelinformation”.

For the case of the CHSWIE status=11 (FIG. 23A), when the CSE has apriori knowledge of the LTRC of the CDE, either correct or incorrect,its transmitted eRTX frame always carries a non-empty CHSWIE. As aresult, the CHSWIE status bits of the CC the in CHSWIE are loaded with11.

As a first exemplary case, assume that the Reason Code has been set to000. This refers to temporary switching with only one appended CIsub-field. When this configuration is used in an eRTX control frame, theCI carries LTRC channel information of the CDE. To establish a linklayer connection with a CME, the CSE needs to switch to the LTRC of theintended CDE. By transmitting an eRTX frame, the CSE sends its requestto the CDE and, at the same time, it informs its one-hop cognitive meshneighbors of its temporary transition to another non-ISM channel. Inthis case the LTRC channel information of the CDE should be included inthe CHSWIE of the eRTX. On the other hand when the Reason Code is loadedwith 010, not only the LTRC of the CDE but also the LTRC channelinformation of the CSE is included in the CHSWIE of the eRTX, where bothappended LTRCs (CDE and CSE) are based on local knowledge of the CSE. Itshould be noted that inclusion of the LTRC channel information of theCDE in eRTX control frames is considered mandatory, while enclosure ofthe LTRC channel information of the CSE is considered to be optional.Also note that for the case of 000 the size of CHSWIE is seven byteswhile for the case of 010 it is eleven bytes.

For the case of an eCTX, when the Reason Code is loaded with 000, thesingle appended CI carries the LTRC of the CSE. Basically, when theknowledge of the CDE concerning the LTRC channel information of the CSEis incorrect, the technique to obtain the correct information is to useintegrate the LTRC channel information of the CSE in the received eRTX.Actually, the correct information can be obtained via the received eRTXif the CSE has previously included its LTRC channel information in thepreceding eRTX. When the CDE notices that its knowledge about the LTRCof the CSE is incorrect, it preferably makes the required corrections toits local databases as soon as possible. In fact, the CDE will be unableto be informed about its incorrect knowledge unless the CSE includes itsLTRC channel information in the eRTX frame to be sent to CDE (recallthat inclusion of the LTRC channel information of the CSE in the eRTX isoptional). In this way the CDE is enabled to determine that itsknowledge regarding the LTRC of the CSE is incorrect and needs to becorrected. In addition to the importance of local knowledge correction,the CDE is also mandated to inform its one-hop CMNs of the correct LTRCchannel information of the CSE. In fact, it is possible that the CDE hasalready distributed its incorrect knowledge among its one-hop CMNs,resulting in further undesirable distribution of theinconsistent/incorrect information. Therefore, when the CDE (byreception of an eRTX frame carrying the LTRC channel information of theCSE) is notified of its incorrect knowledge, it is required to place thecorrect information within its eCTX and send it out over the shared ISMchannel.

As a next case, consider an eCTX with Reason Code equal to 001:temporary switching with only one appended CI sub-field. In this casethe CI carries LTRC channel information of the CDE. When a CME transmitsan eRTX frame over the shared ISM channel, it is required to place theLTRC channel information of its intended CDE within the CHSWIE field ofthe eRTX. If the CDE receives the delivered eRTX and notices erroneousappended information concerning its LTRC, instead of sending the eCTX onits non-ISM LTRC it instead sends out the eCTX over the shared ISMchannel. In addition the CDE places its correct LTRC channel informationin the eCTX to inform the CSE of its incorrect knowledge. In response,the CSE responds with another eRTX on the ISM channel that contains theLTRC correct information. Only after transmission of an eRTX with thecorrect channel information is the CSE allowed to commence its datadelivery over the intended non-ISM channel (i.e., the LTRC of the CDE).

For the case of an eCTX carrying a Reason Code loaded with 010, not onlyis the knowledge of the CSE about the LTRC of the CDE incorrect, but theknowledge of the CDE about the LTRC of the CSE is also incorrect. Inother words, this case includes both above-described scenarios, i.e.,eCTX/000 and eCTX/001. The CDE is required to send the eCTX with boththe LTRC correct channel information for the CSE and its own LTRCcorrect channel information. This frame is delivered on the shared ISMchannel, and the CSE is then also required to send another eRTX frameover the shared ISM channel that contains the correct LTRC channelinformation for the CDE. The CSE then begins sending data frame(s) onthe LTRC of the CDE after completion of sending the second eRTX (plus anadditional SIFS).

Discussed now is the case of CHSWIE status=00 (FIG. 23B).When the CSEhas no a priori knowledge about the LTRC of the CDE, either correct orincorrect, its transmitted eRTX frame carries an empty CHSWIE. As aresult, the CHSWIE status bits of the CC in the CHSWIE are loaded with00. In addition, and as far as the receiver side (i.e., CDE) isconcerned, when both the appended LTRC channel information of the CDE inthe eRTX, and the knowledge of the CDE about the LTRC of the CSE arecorrect, the CDE is allowed to respond by the use of an eCTX transmittedon its own non-ISM LTRC. In this case the CHSWIE of the eCTX is empty,with no further appended CI field.

FIG. 24 shows the regular frame exchange between CSE and CDE when theknowledge of the CSE concerning the LTRC channel information of the CDEis correct. The CSE first initiates a backoff cycle and commencescounting down the backoff counter. Before reaching one, for everycountdown CSE is required to perform carrier sensing only on the sharedISM channel. When counting down from one to zero the CSE is expected toperform carrier sensing on both the ISM and on the LTRC non-ISM channelsof the CDEs. Upon reaching zero the CSE sends an eRTX over the sharedISM channel. Since in this scenario the included information in the eRTXregarding LTRC of the CDE is correct, the CDE responds with an eCTX onits LTRC channel. Subsequently, data and ACK frames are also exchangedover the LTRC of the CDE. As was mentioned above, the scenario shown inFIG. 24 corresponds to the case where the knowledge of the CSE about theLTRC of the CDE is correct. In this scenario the CSE includes only theLTRC information of the CDE in the CHSWIE field of the eRTX which isbeing transmitted over the shared ISM channel. When only the LTRCchannel information of the CDE is included in the eRTX the Duration/IDfield in the eRTX is loaded by eCTX (with 7 bytes CHSWIE)+2×SIFS, whilethe OLD sub-field in the CHSWIE is loaded by eCTX (with 1 byteCHSWIE)+DATA+ACK+3×SIFS. In this scenario the transmitted eCTX on LTRCof the CDE carries an empty CHSWIE for which the Duration/ID field isloaded by 00, and the OLD sub-field in the CHSWIE is loaded byDATA+ACK+2×SIFS. The reason that the CSE reserves the ISM channel for atime period equal to eCTX (with 7 bytes CHSWIE)+2×SIFS is due to thefact that the CSE should take into account the case when its knowledgeof the LTRC of the CDE is totally incorrect, and thus where the intendedCDE responds with an eCTX on the shared ISM channel accompanied by anon-empty 7 byte CHSWIE with the correct LTRC channel information forthe CDE. In this case the shared ISM channel should have been reservedby CSE beforehand to prevent any possible loss of channel control. Ifthe ISM channel is reserved for less than the aforementioned period, itis possible that another ME may acquire control of the shared ISMchannel, and the above tagged CSE then needs to re-initiate the entireeRTX/eCTX negotiation phase from the beginning.

FIG. 25 shows the case when only the LTRC channel information of the CDEis included in the eRTX, while the knowledge of the CSE of the LTRC ofthe CDE is incorrect.

In this case the CSE appends only the LTRC channel information for theintended CDE in the CHSWIE of the eRTX. In addition, the knowledge ofthe CSE about LTRC of the CDE is incorrect. As a result, the CDEresponds with an eCTX on the shared ISM channel to inform the CSE of itsincorrect knowledge regarding the LTRC of the CDE. When the CSE receivesthe eCTX from the shared ISM channel it is accordingly notified aboutits incorrect knowledge and, as a result, it sends out another eRTX onthe common ISM channel with corrected LTRC information of the CDE. Uponsuccessful reception of the second eRTX with the corrected LTRCinformation, and after an additional SIFS, the CSE is allowed to starttransmission of its data frames on the (correct) LTRC of the CDE. As itwas pointed out above, when only the LTRC channel information of the CDEis included in eRTX the Duration/ID field in the eRTX is loaded with theeCTX (with 7 bytes CHSWIE)+2×SIFS, while the OLD sub-field in the CHSWIEis loaded with eCTX (with 1 byte CHSWIE)+DATA+ACK+3×SIFS. On the otherhand, based on this scenario the transmitted eCTX on the shared ISMchannel carries a CHSWIE loaded with the correct LTRC channelinformation of the CDE for which the Duration/ID field is loaded witheRTX (with 7 bytes CHSWIE)+SIFS and the OLD sub-field in the CHSWIE isloaded with eRTX (with 7 bytes CHSWIE)+DATA+ACK+3×SIFS. For the secondeRTX the Duration/ID field is loaded with 00, while the OLD sub-field isloaded with DATA+ACK+2×SIFS.

FIG. 26 shows the channel reservation using eRTX and eCTX when the CSEhas no a priori knowledge of the LTRC of the CDE. When the CSE has no apriori knowledge about the LTRC of the intended CDE it simply sends aneRTX frame with an empty CHSWIE on the shared ISM channel to inform theCDE of its desire to establish a link layer connection. Upon receptionof an eRTX frame with an empty CHSWIE the CDE replies with an eCTX onthe shared ISM channel carrying its current LTRC channel information.When the CSE receives the eCTX it sends another eRTX on the shared ISMchannel accompanied by LTRC channel information of the CDE in the CHSWIEfield. After completion of second eRTX transmission the CSE commencesdata delivery on the targeted non-ISM channel (i.e., on the LTRC of theCDE).

In the case depicted by FIG. 26 the Duration/ID field of first eRTX isloaded with eCTX (with 7 bytes CHSWIE)+2×SIFS while the OLD sub-field inthe CHSWIE is loaded with eCTX (with 7 bytes CHSWIE)+eRTX (with bytesCHSWIE)+DATA+ACK+4×SIFS. The transmitted eCTX on the shared ISM channelcarries a CHSWIE loaded with the LTRC channel information of the CDE forwhich the Duration/ID field is loaded with eRTX (with 7 bytesCHSWIE)+SIFS and the OLD sub-field in the CHSWIE is loaded with eRTX(with 7 bytes CHSWIE)+DATA+ACK+3×SIFS. For the second eRTX theDuration/ID field is simply loaded with 00, while the OLD sub-field isloaded with DATA+ACK+2×SIFS.

FIG. 27 shows the case where the CSE includes both CDEs and LTRC channelinformation in the eRTX frame to be delivered on the shared ISM channel.In this case it is assumed that the appended LTRC channel information ofthe CDE in the eRTX is correct, while the knowledge of the CDE about theLTRC of the CSE is incorrect. Since the CSE has included its LTRCchannel information in the eRTX, the CDE is informed that its knowledgeconcerning the LTRC of the CSE is incorrect. As a result, the CDEresponds using an eCTX delivered on the shared ISM channel appended withthe correct LTRC channel information of the CSE. In response, and aftera SIFS, the CSE commences transmission of data frames over the LTRC ofthe CDE.

For the case shown in FIG. 27 the Duration/ID field of eRTX is loadedwith the eCTX (with 11 bytes CHSWIE)+2×SIFS, while the OLD sub-field inthe CHSWIE is loaded with eCTX (with 1 byte CHSWIE)+DATA+ACK+3×SIFS. Thetransmitted eCTX on the shared ISM channel carries a CHSWIE loaded withthe LTRC channel information of the CSE, for which the Duration/ID fieldis loaded with ‘00’ while the OLD sub-field in the CHSWIE is loaded withDATA+ACK+2×SIFS.

FIGS. 28 and 29 illustrate all possible CHSWIE configurations for botheRTX and eCTX, including their Duration/ID and OLD sub-field setups.

As was described above, a designated control frame referred to as SWinvis defined to be employed for Unicast Welfare Enhancement (UWE) andMulticast Welfare Enhancement (MWE). Note also that the SWinv controlframe may be used as well for inviting cognitive members of a multicastgroup to gather or congregate in a particular non-ISM channel (which maybe totally different than their own respective LTRC channels). Based inlarge part on the UWE concept the CME 40 is allowed to invite itsintended CDEs to gather in a certain non-ISM channel. If the invitationof the CSE is accepted by the entire group of CDEs the CME 40 (i.e., theCSE in this case) is enabled to use frame bursting to achieve asignificantly higher channel throughput (channel utilization) bysuccessively transmitting data frames addressed to the invited CDEs. Forthe multicasting case (i.e., MWE), and since the CME 40 is not allowedto deploy the shared non-ISM channel for cognitive unicast/multicastdata transmission, and further since there is no way to performmulticasting over multiple non-ISM channels at the same time (due to thepresence of the single non-ISM transceiver 44), the multicast CSEinvites members of its intended multicast group to gather in theparticular non-ISM channel.

FIG. 30 illustrates the detailed frame format of the SWinv and its CHSWIE. It may be noticed that the design of the SWinv frame structureenables legacy 802.11 and 802.11s equipment to interpret all of theappended legacy fields without difficulty. Note that between theDuration/ID and transmitter address (TA) fields the first receiveraddress (RA) is positioned. This address can be a unicast, a multicast,or a broadcast MAC address. In CHSWIE field up to two CI fields may beincluded, depending on the application and addressing scenario.Subsequent to the CHSWIE field up to three further RAs may be included.These RAs can be either unicast or multicast MAC addresses. The SWinv isterminated with a conventional FCS. TA represents the MAC address of theinviting CME 40, while the RAs hold invited CME MAC addresses. In FIG.30 the CC sub-field of CHSWIE in the SWinv is also illustrated. Thefirst two bits of the CC are dedicated to a “No. of Extra RA Fields”.Using these two bits the number of additional RA fields that areincluded in the SWinv after the CHSWIE is specified to the receiver. Forexample, 00: No extra RA fields, 01: one extra RA fields, 10: two extraRA fields, 11: three extra RA fields. Several following bits arepresently not used. As before, the Permanent/Temporary Switching Flag,No. of Channel Fields, and Application Bit are used to differentiatebetween diverse unicast/multicast scenarios. The Permanent/TemporarySwitching Flag specifies the type of switching for the case ofmulticasting. It should be noted that for unicast switching (i.e., UWE),channel switching is always performed permanently. As a result the OLDsub-field in the CHSWIE is not needed to declare the amount of timeinvited CDEs are required to switch to the destination non-ISM channel.Therefore, if the planned switching is intended for only the UWE, theOLD sub-field may be simply loaded by FFFF Hex. On the other hand, formulticast-related switching scenarios the OLD sub-field may be set toany needed value. If the Permanent/Temporary Switching Flag is loadedwith a one, then the OLD sub-field is preferably loaded with FFFF Hex.

Note that by the use of the SWinv it is possible to combine multicastand unicast switching invitations into a single control frame. As aresult the incurred overhead due to successive switching invitations canbe reduced. Since it is possible to append both multicast and unicastswitching invitations into a single SWinv at the same time, a pluralityof CI fields are used to carry the destination channel relatedinformation for both the multicast and unicast cases.

A description is now provided of exemplary different use caseapplications of the SWinv control frame.

A first use case relates to multicast temporary channel switching. Whenthe CME 40 intends to invite members of a multicast group to switchtemporarily to a particular non-ISM channel it sends a SW inv with No.of Extra RA Fields set to ‘00’, Permanent/Temporary Switching Flag 15set to ‘0’ (indicating Temporary), No. of Channel Fields 16 set to ‘0’,and the OLD sub-field loaded with a value between 0 and FFFF Hex. Themulticast physical (MAC) address is placed in the first RA field (the RAfield between the Duration/ID and TA fields). The destination non-ISMchannel information is loaded into the single appended CI sub-field inCHSWIE. OLD is loaded by MULTICAST_DATA+SIFS. The transmitter address(TA) is loaded with the CSE (inviting ME) MAC address. The Duration/IDfield of SWinv is loaded with ‘00’. Upon transmission of the SWinv onthe shared ISM channel, plus an extra SIFS, the multicast CSE commencesdelivering the multicast data frame(s) on the destination non-ISMchannel. No acknowledgment is required to be returned by CDEs aftercompletion of multicast data transmission. In addition, invited CDEs arenot required to transmit a CHSW control frame when switching to theintended destination channel. FIG. 31 shows the timing and frameexchange pattern for multicast invitation/transmission in more detail.

In FIG. 31 the multicast CSE commences a backoff cycle based on thelegacy DCF access scheme. Before the backoff counter reaches one the CSEperforms carrier sensing only on the shared ISM channel, while whencounting down from one to zero it performs the carrier sensing procedurefor both the shared ISM and the destination non-ISM channels. When thechannels are sensed as being idle for a period of time equal to at leastDIFS, the CSE transmits a SWinv on the shared ISM channel to invite twomembers of a multicast group (i.e., D1 and D2) to switch to thedestination non-ISM channel, C3. Both invited CDEs switch to the C3channel to receive the multicast data frame. Upon completion of datareception, both CDEs switch back to their initial LTRCs.

A second use case relates to multicast permanent channel switching. Whenthe CME 40 intends to invite members of a multicast group to switchpermanently to a particular non-ISM channel, it sends a SWinv with No.of Extra RA Fields set to ‘00’, Permanent/Temporary Switching Flag setto >1=, and No. of Channel Fields set to ‘0’. The multicast MAC physicaladdress is placed in the first RA field. The destination non-ISM channelinformation is loaded into the single appended CI sub-field in the CHSWIE. The TA is loaded with the CSE (inviting ME) MAC address. No extra RAfield is appended after the CHSW IE. In this case, two differentstrategies may be used for multicast permanent channel switching.

In the first strategy, which may be referred to as Mode I MulticastPermanent Channel Switching, the multicast CSE initiates a backoff cyclebased on the legacy DCF access scheme. Before the backoff counterreaches one the CSE performs carrier sensing only on the shared ISMchannel, while when counting down from one to zero the CSE performs thecarrier sensing procedure for both the shared ISM and the destinationnon-ISM channels. When the channels are sensed idle for at least DIFS,the CSE transmits a SWinv on the shared ISM channel to invite multicastmembers to switch (permanently) to the destination non-ISM channel. Inthis mode the Duration/ID field is loaded with 00. In addition, the OLDsub-field of the CHSWIE in the SWinv is also loaded with 00. To informthe CDEs that the intended multicast permanent channel switching isinitiated based on Mode I the CSE loads the Application Bit of the CCsub-field in the SWinv control frame with zero. Upon completion of theSWinv transmission, the CSE loads a switching timeout timer with amaximum possible busy period in the shared ISM channel (see IEEE802.11/1999 standard) and waits for the CDEs to switch to thedestination channel. Whenever an invited CDE decides to switch to thedestination channel, it is required to perform carrier sensing on theshared ISM channel. Each invited CDE sends a CHSW frame over the ISMchannel to inform its one-hop cognitive mesh neighbors (and speciallythe multicast CSE) that it is permanently switching to the new channel,and is thus selecting it as its new LTRC. Upon expiration of theswitching timeout timer CSE commences transmission of multicast dataframes using a regular RTX control frame with the RA loaded with themulticast MAC address. For transmission of the RTX frame the CSE isperforms carrier sensing on both shared ISM and the destination non-ISMchannels. FIG. 32 illustrates the above described interactions in moredetail.

In the second strategy, which may be referred to as Mode II MulticastPermanent Channel Switching (Fast CHSW), the multicast CSE initiates abackoff cycle based on the legacy DCF access scheme. Before the backoffcounter reaches one the CSE performs carrier sensing only on the sharedISM channel, while when counting down from one to zero the CSE performsthe carrier sensing procedure for both the shared ISM and thedestination non-ISM channels. When the channels are sensed idle for atleast DIFS, the CSE transmits a SWinv on the shared ISM channel toinvite multicast members to permanently switch to the destinationchannel. In this second mode the Duration/ID field of the SWinv isloaded with 00 while the OLD sub-field of the CHSWIE is loaded withMULTICAST_DATA+SIFS. To inform the CDEs that the intended multicastpermanent channel switching is initiated based on Mode II the CSE loadsthe Application Bit of the CC sub-field in the SWinv control frame witha one. In this mode, after completion of SWinv transmission plus anSIFS, all CDEs are required to switch to the destination non-ISMchannel. Switching to the new non-ISM channel is accomplished beforeinforming one-hop cognitive mesh neighbors of selecting the destinationchannel as the new LTRC using the designated CHSW control frames. Inparallel with the multicast data frame reception the multicast CDEs mayalso contend for the shared ISM channel to transmit the required CHSWframes to inform their one-hop neighbors of the selection of the non-ISMchannel as their new LTRC. In this mode there is no need for the CSE toinitiate the switching timeout timer. This type of multicast switchingis well suited for use in fast channel switching cases, such as when themulticast MSDU(s) are sensitive to the incurred access/transmissiondelay (i.e., for voice or video traffic). FIG. 33 illustrates thisabove-described use case.

A third use case relates to unicast welfare enhancement (UWE). When theCME 40 intends to invite another single CME 40 to permanently switch toa particular non-ISM channel it sends a SW inv with the No. of Extra RAFields set to 00, the Permanent/Temporary Switching Flag set to 1, theNo. of Channel Fields set to 0 and the OLD sub-field loaded with FFFFHex. When the CME intends to invite a plurality of other CMEs 40 topermanently switch to a particular non-ISM channel it sends a SWinv withthe No. of Extra RA Fields loaded with 01, 10, or 11, thePermanent/Temporary Switching Flag set to 1, the No. of Channel Fieldsset to 0 and the OLD sub-field loaded with FFFF Hex. The destinationnon-ISM channel information is loaded into a single appended CIsub-field in the CHSWIE. The TA is loaded with the address of the CSE(inviting ME). The Duration/ID field of SWinv is loaded with 00. By theuse of the SWinv the CSE is able to invite up to four CMEs to switch tothe destination non-ISM channel. In this case the Application Bit in theCC sub-field is not used. Subsequent to receiving the SWinv the invitedCDEs contend for the shared ISM channel to transmit CHSW frames in orderto inform their one-hop cognitive neighbors of the permanent switch tothe new non-ISM channel.

A fourth use case relates to combined Multicast/Unicast channelswitching. In this case the CSE invites a multicast group and a set ofunicast CMEs to permanently switch to either one or two non-ISMchannel(s). The multicast MAC address is loaded into the first RA fieldbetween Duration/ID and TA fields, while the remaining three RAaddresses may be used for the unicast channel switching cases. Inaddition, the first CI sub-field in the CHSWIE is used for multicastchannel switching and the second CI is utilized for the unicast channelswitching case. As in the use cases described above, the Duration/IDfield is loaded with 00. The OLD sub-field in the CHSWIE is loaded witheither 00 or MULTICAST_DATA+SIFS, depending on the type of multicastingchannel switching: Mode I or Mode II. Using the Application Bit in theCC, the type (or mode) of the multicast switching is specified. Based onthe specified type of multicast switching the OLD sub-field is loadedwith the appropriate value, i.e., 00 (Mode I) or MULTICAST_DATA+SIFS(Mode II). The subsequent channel activity is the same as multicastswitching explained above, and is coordinated based on the switchingmode: I or II. The OLD sub-field is not used for the appended unicastcase, instead it is used for multicast switching and loaded according tothe multicast mode. The unicast CDEs are required to transmit a CHSWframe over the shared ISM channel if they agree to switch their LTRC tothe advertised destination channel. FIG. 34 illustrates an example forthis case.

It can be appreciated that the embodiments described with reference toFIGS. 18-34 provide a further novel frequency agile medium accesscontrol protocol capable of coordination of concurrent multi-channeldata communications in a distributed fashion. These embodiments mayemploy the distributed multi-channel cognitive MAC protocol for the802.11 wireless LANs (an enhanced MAC or eMAC) which was described inreference to FIGS. 1-17. These embodiments provide unicast/multicastwelfare enhancement, and a practical approach to reduce the incurredoverhead on the shared ISM channel due to cognitive mesh entitiescontrol/management frame exchange. In addition, medium access delayexperienced by cognitive mesh entities is reduced.

Based on the foregoing it should be apparent that the exemplaryembodiments provide a method, apparatus and computer program product(s)to enhance the operation of wireless networks that include cognitiveradio apparatus, such as mobile stations and mesh elements.

FIG. 35 is a logic flow diagram that illustrates the operation of amethod, and a result of execution of computer program instructions, inaccordance with the exemplary embodiments. At Block 35A there is a stepof sending a message from a first cognitive radio apparatus to at leastone second cognitive radio apparatus, the message being sent over afirst communication channel and comprises an advertisement of at leastone second communication channel for use in sending data from the firstcognitive radio apparatus to the at least one second cognitive radioapparatus. At Block 35B there is a step of receiving a reply from the atleast one second cognitive radio apparatus over the first communicationchannel, the reply comprising one of an acceptance of one of the atleast one second communication channels, a rejection of the at least onesecond communication channel and an advertisement of at least one thirdcommunication channel, or a rejection of the at least one secondcommunication channel without an advertisement of at least one thirdcommunication channel. At Block 35C there is a step of transmitting thedata from the first cognitive radio apparatus to the at least one secondcognitive radio apparatus over an agreed upon one of the second or thirdchannels.

In the method, and the result of execution of computer programinstructions as in the previous paragraph, where in a case where thereply is a rejection of the at least one second communication channeland the advertisement of at least one third communication channel,further comprising sending a response from the first cognitive radioapparatus to the second cognitive radio apparatus over the firstcommunication channel, the response comprising one of an acceptance ofone of the at least one third communication channels or a rejection ofthe at least one third communication channel.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, where the reply comprisesone of a reason for the acceptance or a reason for the rejection.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, where the firstcommunication channel is a common channel in an ISM frequency band thatis used by cognitive radio apparatus and by non-cognitive radioapparatus.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, where the first cognitiveradio apparatus operates in one of a power saving mode enabled state ora power saving mode disabled state.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, where the first cognitiveradio apparatus comprises a first transceiver for communication over thefirst communication channel and a second frequency agile transceiver forcommunication over the second or third communication channels, furthercomprising a first task list associated with the first transceiver and asecond task list associated with the second transceiver, each task listcomprising at any given time one or both of reception tasks andtransmission tasks and, for at least the second task list, acommunication channel associated with each task.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, where tasks in a given oneof the task lists are prioritized, where reception tasks are assigned ahigher priority than transmission tasks.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, further comprisingscheduling tasks so as to use, if possible, a same communication channelfor more than one task.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, further comprisingscheduling tasks so as to use, if possible, a same communication channelfor two reception tasks.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, further comprisingscheduling tasks so as to use, if possible, a same communication channelfor two transmission tasks.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, further comprisingscheduling tasks so as to use, if possible, a same communication channelfor a reception task and for a transmission task.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, further comprisingscheduling tasks so as to use a communication channel for a multicasttransmission task to a plurality of second cognitive radio apparatus.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, further comprisingscheduling tasks so as to use a communication channel for a multicasttransmission task to a plurality of second cognitive radio apparatus,and the same communication channel for a unicast transmission to atleast one further cognitive radio apparatus.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, where the second and thirdcommunication channels are in a non-ISM frequency band, and where adecision to accept or reject a particular channel is based at least inpart on a result of spectrum sensing in the non-ISM frequency band todetect an appearance of a primary user.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, where an advertisedcommunication channel is accepted if it is not a channel in which aprimary user appeared, and it has satisfactory spectrum quality results.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, further comprising operatinga cognitive medium access control entity that comprises a LastSuccessfully Experienced Channel (LSEC) table, a Primary User Appearance(PUA) table, and a Transient Zone that buffers identifications oflocally and remotely discovered non-ISM channels, where each channelidentified in LSEC and PUA table entries includes an associated timeindex having a value that changes periodically and that controlspotential usage of the channels identified in the LSEC and PUA tables.

In the method, and the result of execution of computer programinstructions as in the previous paragraph, where the value of the timeindex is changed every Beacon Interval.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, where the time index valueof a particular channel is reset to zero when the channel is placed inthe LSEC table, where the time index value is periodically incremented,and where the channel is not available to be reused until the time indexvalue reaches some predetermined non-zero value.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, where the time index valueof a particular channel is set to some predetermined value when thechannel is placed in the PUA table, where the time index value isperiodically decremented, and where the channel is removed from the PUAtable when the time index value reaches zero.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, where advertisements of thesecond and third communication channels each comprise fields forspecifying an identification of a center frequency and a regulatoryclass.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, where the first cognitiveradio apparatus comprises a first transceiver for communication over thefirst communication channel, where the first communication channel is acommon channel in an ISM frequency band that is used by cognitive radioapparatus and by non-cognitive radio apparatus, and a second frequencyagile transceiver for communication over at least one communicationchannel in a non-ISM frequency band, further comprising sending amessage over the first communication channel to the at least one secondcognitive radio apparatus that also comprises first and secondtransceivers, the message instructing the second cognitive radioapparatus to one of switch temporarily or permanently to a particularcommunication channel in the non-ISM frequency band.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, where in one mode ofoperation the second cognitive radio apparatus acknowledges the messageover the first communication channel before switching to the particularcommunication channel in the non-ISM frequency band, and where inanother mode of the operation the second cognitive radio apparatusacknowledges the message over the first communication channel afterswitching to the particular communication channel in the non-ISMfrequency band.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, further comprising sendingat least one of multicast data and unicast data over the particularcommunication channel in the non-ISM frequency band.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, where the message invites amulticast group of second cognitive radio apparatus to switchtemporarily to a particular non-ISM communication channel.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, where the message invites amulticast group of second cognitive radio apparatus to switchpermanently to a particular non-ISM communication channel.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, where the message invites asingle second cognitive radio apparatus to switch temporarily to aparticular non-ISM communication channel.

In the method, and the result of execution of computer programinstructions as in the previous paragraphs, where the message invites amulticast group of second cognitive radio apparatus and a single secondcognitive radio apparatus to switch permanently to one or more than oneparticular non-ISM communication channels.

The various blocks shown in FIG. 35 may be viewed as method steps,and/or as operations that result from operation of computer programcode, and/or as a plurality of coupled logic circuit elementsconstructed to carry out the associated function(s).

In general, the various exemplary embodiments may be implemented inhardware or special purpose circuits, software, logic or any combinationthereof. For example, some aspects may be implemented in hardware, whileother aspects may be implemented in firmware or software which may beexecuted by a controller, microprocessor or other computing device,although the disclosed embodiments are not limited thereto. Whilevarious aspects of the exemplary embodiments may be illustrated anddescribed as block diagrams, flow charts, or using some other pictorialrepresentation, it is well understood that these blocks, apparatus,systems, techniques or methods described herein may be implemented in,as non-limiting examples, hardware, software, firmware, special purposecircuits or logic, general purpose hardware or controller or othercomputing devices, or some combination thereof.

As such, it should be appreciated that at least some aspects of theexemplary embodiments may be practiced in various components such asintegrated circuit chips and modules. The design of integrated circuitsis by and large a highly automated process. Complex and powerfulsoftware tools are available for converting a logic level design into asemiconductor circuit design ready to be fabricated on a semiconductorsubstrate. Such software tools can automatically route conductors andlocate components on a semiconductor substrate using well establishedrules of design, as well as libraries of prestored design modules. Oncethe design for a semiconductor circuit has been completed, the resultantdesign, in a standardized electronic format (e.g., Opus, GDSII, or thelike) may be transmitted to a semiconductor fabrication facility forfabrication as one or more integrated circuit devices.

Various modifications and adaptations to the foregoing exemplaryembodiments may become apparent to those skilled in the relevant arts inview of the foregoing description, when read in conjunction with theaccompanying drawings. However, any and all modifications will stillfall within the scope of the non-limiting and exemplary embodiments.

For example, while the exemplary embodiments have been described abovein the context of the IEEE 802.11 type of system, it should beappreciated that the exemplary embodiments are not limited for use withonly this one particular type of wireless communication system, and thatthey may be used to advantage in other wireless communication systems.Further, all of the various specific references to specific frequencybands and channels and channel numbers, the number of bits in certainframe fields, the names of these certain bits and fields, the orderingof these fields, the number of certain fields within a given frame andthe like are meant to be exemplary, and are not to be construed aslimitations upon the implementation and practice of the variousexemplary embodiments.

It should be noted that the terms “connected,” “coupled,” or any variantthereof, mean any connection or coupling, either direct or indirect,between two or more elements, and may encompass the presence of one ormore intermediate elements between two elements that are “connected” or“coupled” together. The coupling or connection between the elements canbe physical, logical, or a combination thereof. As employed herein twoelements may be considered to be “connected” or “coupled” together bythe use of one or more wires, cables and/or printed electricalconnections, as well as by the use of electromagnetic energy, such aselectromagnetic energy having wavelengths in the radio frequency region,the microwave region and the optical (both visible and invisible)region, as several non-limiting and non-exhaustive examples.

Furthermore, some of the features of the various non-limiting andexemplary embodiments may be used to advantage without the correspondinguse of other features. As such, the foregoing description should beconsidered as merely illustrative of the principles, teachings andexemplary embodiments, and not in limitation thereof.

1. A method, comprising; sending a message from a first cognitive radioapparatus to at least one second cognitive radio apparatus during anegotiation phase to determine a channel to be used for sending datafrom the first cognitive radio apparatus to the at least one secondcognitive radio apparatus, the message being sent over a firstcommunication channel and comprising an advertisement of at least onesecond communication channel for use in sending the data from the firstcognitive radio apparatus to the at least one second cognitive radioapparatus, the advertisement comprising a correspondingproposition/evaluation bit for each of the at least one secondcommunication channel; receiving a reply from the at least one secondcognitive radio apparatus over the first communication channel, thereply comprising one of an acceptance of one of the at least one secondcommunication channels with the corresponding proposition/evaluation bitfrom the advertisement, a rejection of the at least one secondcommunication channel and an advertisement of at least one thirdcommunication channel, and a rejection of the at least one secondcommunication channel without an advertisement of at least one thirdcommunication channel; and transmitting the data from the firstcognitive radio apparatus to the at least one second cognitive radioapparatus over an agreed upon one of the second or third communicationchannels in response to a completion of the negotiation phase.